diff --git a/.travis.yml b/.travis.yml
index 57b7cd8..6ab4fe7 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -8,12 +8,6 @@ rvm:
   - jruby-19mode
   - rbx-2
 gemfile:
-  - gemfiles/rubocop_0.14.1.gemfile
-  - gemfiles/rubocop_0.15.0.gemfile
-  - gemfiles/rubocop_0.16.0.gemfile
-  - gemfiles/rubocop_0.17.0.gemfile
-  - gemfiles/rubocop_0.18.1.gemfile
-  - gemfiles/rubocop_0.19.1.gemfile
   - gemfiles/rubocop_0.20.1.gemfile
   - gemfiles/rubocop_0.21.0.gemfile
   - gemfiles/rubocop_0.22.0.gemfile
@@ -27,34 +21,6 @@ gemfile:
   - gemfiles/rubocop_0.30.1.gemfile
 matrix:
   exclude:
-    - rvm: 2.1.6
-      gemfile: gemfiles/rubocop_0.14.1.gemfile
-    - rvm: 2.1.6
-      gemfile: gemfiles/rubocop_0.15.0.gemfile
-    - rvm: 2.1.6
-      gemfile: gemfiles/rubocop_0.15.0.gemfile
-    - rvm: 2.1.6
-      gemfile: gemfiles/rubocop_0.16.0.gemfile
-    - rvm: 2.1.6
-      gemfile: gemfiles/rubocop_0.17.0.gemfile
-    - rvm: 2.1.6
-      gemfile: gemfiles/rubocop_0.18.1.gemfile
-    - rvm: 2.1.6
-      gemfile: gemfiles/rubocop_0.19.1.gemfile
-    - rvm: 2.2.2
-      gemfile: gemfiles/rubocop_0.14.1.gemfile
-    - rvm: 2.2.2
-      gemfile: gemfiles/rubocop_0.15.0.gemfile
-    - rvm: 2.2.2
-      gemfile: gemfiles/rubocop_0.15.0.gemfile
-    - rvm: 2.2.2
-      gemfile: gemfiles/rubocop_0.16.0.gemfile
-    - rvm: 2.2.2
-      gemfile: gemfiles/rubocop_0.17.0.gemfile
-    - rvm: 2.2.2
-      gemfile: gemfiles/rubocop_0.18.1.gemfile
-    - rvm: 2.2.2
-      gemfile: gemfiles/rubocop_0.19.1.gemfile
     - rvm: 2.2.2
       gemfile: gemfiles/rubocop_0.20.1.gemfile
     - rvm: 2.2.2
diff --git a/Appraisals b/Appraisals
index 4f4f199..34458ab 100644
--- a/Appraisals
+++ b/Appraisals
@@ -1,10 +1,4 @@
 [
-  '0.14.1',
-  '0.15.0',
-  '0.16.0',
-  '0.17.0',
-  '0.18.1',
-  '0.19.1',
   '0.20.1',
   '0.21.0',
   '0.22.0',
diff --git a/README.md b/README.md
index 1bda899..6cd932b 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,7 @@
 # RuboCop Checkstyle Formatter
 
 A formatter for [RuboCop](https://github.com/bbatsov/rubocop) that outputs in checkstyle format.
-It requires RuboCop version 0.14.0 or above.
+It requires RuboCop version 0.20.1 or above.
 
 [![Build Status](https://travis-ci.org/eitoball/rubocop-checkstyle_formatter.svg?branch=master)](https://travis-ci.org/eitoball/rubocop-checkstyle_formatter)
 
@@ -22,7 +22,7 @@ Or install it yourself as:
 ## Usage
 
     $ rubocop --require rubocop/formatter/checkstyle_formatter --format RuboCop::Formatter::CheckstyleFormatter
-    
+
 I use this formatter in Jenkins with [Violations plugin](https://wiki.jenkins-ci.org/display/JENKINS/Violations).
 As a part of build, I execute rubocop as shell script like:
 
diff --git a/gemfiles/rubocop_0.14.1.gemfile b/gemfiles/rubocop_0.14.1.gemfile
deleted file mode 100644
index 36883f4..0000000
--- a/gemfiles/rubocop_0.14.1.gemfile
+++ /dev/null
@@ -1,7 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "rubocop", "0.14.1"
-
-gemspec :path => "../"
diff --git a/gemfiles/rubocop_0.14.1.gemfile.lock b/gemfiles/rubocop_0.14.1.gemfile.lock
deleted file mode 100644
index 546de25..0000000
--- a/gemfiles/rubocop_0.14.1.gemfile.lock
+++ /dev/null
@@ -1,46 +0,0 @@
-PATH
-  remote: ../
-  specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
-
-GEM
-  remote: https://rubygems.org/
-  specs:
-    appraisal (1.0.0)
-      bundler
-      rake
-      thor (>= 0.14.0)
-    ast (2.0.0)
-    diff-lcs (1.2.5)
-    parser (2.1.9)
-      ast (>= 1.1, < 3.0)
-      slop (~> 3.4, >= 3.4.5)
-    powerpack (0.0.9)
-    rainbow (2.0.0)
-    rake (10.3.2)
-    rspec (2.14.1)
-      rspec-core (~> 2.14.0)
-      rspec-expectations (~> 2.14.0)
-      rspec-mocks (~> 2.14.0)
-    rspec-core (2.14.8)
-    rspec-expectations (2.14.5)
-      diff-lcs (>= 1.1.3, < 2.0)
-    rspec-mocks (2.14.6)
-    rubocop (0.14.1)
-      parser (~> 2.0)
-      powerpack (~> 0.0.6)
-      rainbow (>= 1.1.4)
-    slop (3.5.0)
-    thor (0.19.1)
-
-PLATFORMS
-  ruby
-
-DEPENDENCIES
-  appraisal (~> 1.0.0)
-  bundler (~> 1.3)
-  rake (~> 10.1)
-  rspec (~> 2.14.0)
-  rubocop (= 0.14.1)
-  rubocop-checkstyle_formatter!
diff --git a/gemfiles/rubocop_0.15.0.gemfile b/gemfiles/rubocop_0.15.0.gemfile
deleted file mode 100644
index 23d4e2f..0000000
--- a/gemfiles/rubocop_0.15.0.gemfile
+++ /dev/null
@@ -1,7 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "rubocop", "0.15.0"
-
-gemspec :path => "../"
diff --git a/gemfiles/rubocop_0.15.0.gemfile.lock b/gemfiles/rubocop_0.15.0.gemfile.lock
deleted file mode 100644
index 20663bf..0000000
--- a/gemfiles/rubocop_0.15.0.gemfile.lock
+++ /dev/null
@@ -1,46 +0,0 @@
-PATH
-  remote: ../
-  specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
-
-GEM
-  remote: https://rubygems.org/
-  specs:
-    appraisal (1.0.0)
-      bundler
-      rake
-      thor (>= 0.14.0)
-    ast (2.0.0)
-    diff-lcs (1.2.5)
-    parser (2.1.9)
-      ast (>= 1.1, < 3.0)
-      slop (~> 3.4, >= 3.4.5)
-    powerpack (0.0.9)
-    rainbow (2.0.0)
-    rake (10.3.2)
-    rspec (2.14.1)
-      rspec-core (~> 2.14.0)
-      rspec-expectations (~> 2.14.0)
-      rspec-mocks (~> 2.14.0)
-    rspec-core (2.14.8)
-    rspec-expectations (2.14.5)
-      diff-lcs (>= 1.1.3, < 2.0)
-    rspec-mocks (2.14.6)
-    rubocop (0.15.0)
-      parser (~> 2.0)
-      powerpack (~> 0.0.6)
-      rainbow (>= 1.1.4)
-    slop (3.5.0)
-    thor (0.19.1)
-
-PLATFORMS
-  ruby
-
-DEPENDENCIES
-  appraisal (~> 1.0.0)
-  bundler (~> 1.3)
-  rake (~> 10.1)
-  rspec (~> 2.14.0)
-  rubocop (= 0.15.0)
-  rubocop-checkstyle_formatter!
diff --git a/gemfiles/rubocop_0.16.0.gemfile b/gemfiles/rubocop_0.16.0.gemfile
deleted file mode 100644
index 56da9b9..0000000
--- a/gemfiles/rubocop_0.16.0.gemfile
+++ /dev/null
@@ -1,7 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "rubocop", "0.16.0"
-
-gemspec :path => "../"
diff --git a/gemfiles/rubocop_0.16.0.gemfile.lock b/gemfiles/rubocop_0.16.0.gemfile.lock
deleted file mode 100644
index 4370374..0000000
--- a/gemfiles/rubocop_0.16.0.gemfile.lock
+++ /dev/null
@@ -1,46 +0,0 @@
-PATH
-  remote: ../
-  specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
-
-GEM
-  remote: https://rubygems.org/
-  specs:
-    appraisal (1.0.0)
-      bundler
-      rake
-      thor (>= 0.14.0)
-    ast (2.0.0)
-    diff-lcs (1.2.5)
-    parser (2.1.9)
-      ast (>= 1.1, < 3.0)
-      slop (~> 3.4, >= 3.4.5)
-    powerpack (0.0.9)
-    rainbow (2.0.0)
-    rake (10.3.2)
-    rspec (2.14.1)
-      rspec-core (~> 2.14.0)
-      rspec-expectations (~> 2.14.0)
-      rspec-mocks (~> 2.14.0)
-    rspec-core (2.14.8)
-    rspec-expectations (2.14.5)
-      diff-lcs (>= 1.1.3, < 2.0)
-    rspec-mocks (2.14.6)
-    rubocop (0.16.0)
-      parser (~> 2.1)
-      powerpack (~> 0.0.6)
-      rainbow (>= 1.1.4)
-    slop (3.5.0)
-    thor (0.19.1)
-
-PLATFORMS
-  ruby
-
-DEPENDENCIES
-  appraisal (~> 1.0.0)
-  bundler (~> 1.3)
-  rake (~> 10.1)
-  rspec (~> 2.14.0)
-  rubocop (= 0.16.0)
-  rubocop-checkstyle_formatter!
diff --git a/gemfiles/rubocop_0.17.0.gemfile b/gemfiles/rubocop_0.17.0.gemfile
deleted file mode 100644
index c98fdd0..0000000
--- a/gemfiles/rubocop_0.17.0.gemfile
+++ /dev/null
@@ -1,7 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "rubocop", "0.17.0"
-
-gemspec :path => "../"
diff --git a/gemfiles/rubocop_0.17.0.gemfile.lock b/gemfiles/rubocop_0.17.0.gemfile.lock
deleted file mode 100644
index ca61e6a..0000000
--- a/gemfiles/rubocop_0.17.0.gemfile.lock
+++ /dev/null
@@ -1,48 +0,0 @@
-PATH
-  remote: ../
-  specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
-
-GEM
-  remote: https://rubygems.org/
-  specs:
-    appraisal (1.0.0)
-      bundler
-      rake
-      thor (>= 0.14.0)
-    ast (2.0.0)
-    diff-lcs (1.2.5)
-    json (1.8.1)
-    parser (2.1.9)
-      ast (>= 1.1, < 3.0)
-      slop (~> 3.4, >= 3.4.5)
-    powerpack (0.0.9)
-    rainbow (1.99.2)
-    rake (10.3.2)
-    rspec (2.14.1)
-      rspec-core (~> 2.14.0)
-      rspec-expectations (~> 2.14.0)
-      rspec-mocks (~> 2.14.0)
-    rspec-core (2.14.8)
-    rspec-expectations (2.14.5)
-      diff-lcs (>= 1.1.3, < 2.0)
-    rspec-mocks (2.14.6)
-    rubocop (0.17.0)
-      json (~> 1.8)
-      parser (~> 2.1.3)
-      powerpack (~> 0.0.6)
-      rainbow (~> 1.99.1)
-    slop (3.5.0)
-    thor (0.19.1)
-
-PLATFORMS
-  ruby
-
-DEPENDENCIES
-  appraisal (~> 1.0.0)
-  bundler (~> 1.3)
-  rake (~> 10.1)
-  rspec (~> 2.14.0)
-  rubocop (= 0.17.0)
-  rubocop-checkstyle_formatter!
diff --git a/gemfiles/rubocop_0.18.1.gemfile b/gemfiles/rubocop_0.18.1.gemfile
deleted file mode 100644
index 4f29433..0000000
--- a/gemfiles/rubocop_0.18.1.gemfile
+++ /dev/null
@@ -1,7 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "rubocop", "0.18.1"
-
-gemspec :path => "../"
diff --git a/gemfiles/rubocop_0.18.1.gemfile.lock b/gemfiles/rubocop_0.18.1.gemfile.lock
deleted file mode 100644
index a1d9622..0000000
--- a/gemfiles/rubocop_0.18.1.gemfile.lock
+++ /dev/null
@@ -1,48 +0,0 @@
-PATH
-  remote: ../
-  specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
-
-GEM
-  remote: https://rubygems.org/
-  specs:
-    appraisal (1.0.0)
-      bundler
-      rake
-      thor (>= 0.14.0)
-    ast (2.0.0)
-    diff-lcs (1.2.5)
-    json (1.8.1)
-    parser (2.1.9)
-      ast (>= 1.1, < 3.0)
-      slop (~> 3.4, >= 3.4.5)
-    powerpack (0.0.9)
-    rainbow (2.0.0)
-    rake (10.3.2)
-    rspec (2.14.1)
-      rspec-core (~> 2.14.0)
-      rspec-expectations (~> 2.14.0)
-      rspec-mocks (~> 2.14.0)
-    rspec-core (2.14.8)
-    rspec-expectations (2.14.5)
-      diff-lcs (>= 1.1.3, < 2.0)
-    rspec-mocks (2.14.6)
-    rubocop (0.18.1)
-      json (>= 1.7.7, < 2)
-      parser (~> 2.1.3)
-      powerpack (~> 0.0.6)
-      rainbow (>= 1.99.1, < 3.0)
-    slop (3.5.0)
-    thor (0.19.1)
-
-PLATFORMS
-  ruby
-
-DEPENDENCIES
-  appraisal (~> 1.0.0)
-  bundler (~> 1.3)
-  rake (~> 10.1)
-  rspec (~> 2.14.0)
-  rubocop (= 0.18.1)
-  rubocop-checkstyle_formatter!
diff --git a/gemfiles/rubocop_0.19.1.gemfile b/gemfiles/rubocop_0.19.1.gemfile
deleted file mode 100644
index 80d79a3..0000000
--- a/gemfiles/rubocop_0.19.1.gemfile
+++ /dev/null
@@ -1,7 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "rubocop", "0.19.1"
-
-gemspec :path => "../"
diff --git a/gemfiles/rubocop_0.19.1.gemfile.lock b/gemfiles/rubocop_0.19.1.gemfile.lock
deleted file mode 100644
index 0def26c..0000000
--- a/gemfiles/rubocop_0.19.1.gemfile.lock
+++ /dev/null
@@ -1,50 +0,0 @@
-PATH
-  remote: ../
-  specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
-
-GEM
-  remote: https://rubygems.org/
-  specs:
-    appraisal (1.0.0)
-      bundler
-      rake
-      thor (>= 0.14.0)
-    ast (2.0.0)
-    diff-lcs (1.2.5)
-    json (1.8.1)
-    parser (2.1.9)
-      ast (>= 1.1, < 3.0)
-      slop (~> 3.4, >= 3.4.5)
-    powerpack (0.0.9)
-    rainbow (2.0.0)
-    rake (10.3.2)
-    rspec (2.14.1)
-      rspec-core (~> 2.14.0)
-      rspec-expectations (~> 2.14.0)
-      rspec-mocks (~> 2.14.0)
-    rspec-core (2.14.8)
-    rspec-expectations (2.14.5)
-      diff-lcs (>= 1.1.3, < 2.0)
-    rspec-mocks (2.14.6)
-    rubocop (0.19.1)
-      json (>= 1.7.7, < 2)
-      parser (~> 2.1.7)
-      powerpack (~> 0.0.6)
-      rainbow (>= 1.99.1, < 3.0)
-      ruby-progressbar (~> 1.4)
-    ruby-progressbar (1.5.1)
-    slop (3.5.0)
-    thor (0.19.1)
-
-PLATFORMS
-  ruby
-
-DEPENDENCIES
-  appraisal (~> 1.0.0)
-  bundler (~> 1.3)
-  rake (~> 10.1)
-  rspec (~> 2.14.0)
-  rubocop (= 0.19.1)
-  rubocop-checkstyle_formatter!
diff --git a/gemfiles/rubocop_0.20.1.gemfile.lock b/gemfiles/rubocop_0.20.1.gemfile.lock
index ab77f8a..052b134 100644
--- a/gemfiles/rubocop_0.20.1.gemfile.lock
+++ b/gemfiles/rubocop_0.20.1.gemfile.lock
@@ -1,8 +1,8 @@
 PATH
   remote: ../
   specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
+    rubocop-checkstyle_formatter (0.2.0)
+      rubocop (>= 0.20.1)
 
 GEM
   remote: https://rubygems.org/
diff --git a/gemfiles/rubocop_0.21.0.gemfile.lock b/gemfiles/rubocop_0.21.0.gemfile.lock
index 780560c..2a39030 100644
--- a/gemfiles/rubocop_0.21.0.gemfile.lock
+++ b/gemfiles/rubocop_0.21.0.gemfile.lock
@@ -1,8 +1,8 @@
 PATH
   remote: ../
   specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
+    rubocop-checkstyle_formatter (0.2.0)
+      rubocop (>= 0.20.1)
 
 GEM
   remote: https://rubygems.org/
diff --git a/gemfiles/rubocop_0.22.0.gemfile.lock b/gemfiles/rubocop_0.22.0.gemfile.lock
index b8ed013..61247b2 100644
--- a/gemfiles/rubocop_0.22.0.gemfile.lock
+++ b/gemfiles/rubocop_0.22.0.gemfile.lock
@@ -1,8 +1,8 @@
 PATH
   remote: ../
   specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
+    rubocop-checkstyle_formatter (0.2.0)
+      rubocop (>= 0.20.1)
 
 GEM
   remote: https://rubygems.org/
diff --git a/gemfiles/rubocop_0.23.0.gemfile.lock b/gemfiles/rubocop_0.23.0.gemfile.lock
index 65a1dec..1a74821 100644
--- a/gemfiles/rubocop_0.23.0.gemfile.lock
+++ b/gemfiles/rubocop_0.23.0.gemfile.lock
@@ -1,8 +1,8 @@
 PATH
   remote: ../
   specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
+    rubocop-checkstyle_formatter (0.2.0)
+      rubocop (>= 0.20.1)
 
 GEM
   remote: https://rubygems.org/
diff --git a/gemfiles/rubocop_0.24.0.gemfile.lock b/gemfiles/rubocop_0.24.0.gemfile.lock
index 2779306..acf20af 100644
--- a/gemfiles/rubocop_0.24.0.gemfile.lock
+++ b/gemfiles/rubocop_0.24.0.gemfile.lock
@@ -1,8 +1,8 @@
 PATH
   remote: ../
   specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
+    rubocop-checkstyle_formatter (0.2.0)
+      rubocop (>= 0.20.1)
 
 GEM
   remote: https://rubygems.org/
diff --git a/gemfiles/rubocop_0.25.0.gemfile.lock b/gemfiles/rubocop_0.25.0.gemfile.lock
index e37f471..197ff36 100644
--- a/gemfiles/rubocop_0.25.0.gemfile.lock
+++ b/gemfiles/rubocop_0.25.0.gemfile.lock
@@ -1,8 +1,8 @@
 PATH
   remote: ../
   specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
+    rubocop-checkstyle_formatter (0.2.0)
+      rubocop (>= 0.20.1)
 
 GEM
   remote: https://rubygems.org/
diff --git a/gemfiles/rubocop_0.26.1.gemfile.lock b/gemfiles/rubocop_0.26.1.gemfile.lock
index 105c726..74280c2 100644
--- a/gemfiles/rubocop_0.26.1.gemfile.lock
+++ b/gemfiles/rubocop_0.26.1.gemfile.lock
@@ -1,8 +1,8 @@
 PATH
   remote: ../
   specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
+    rubocop-checkstyle_formatter (0.2.0)
+      rubocop (>= 0.20.1)
 
 GEM
   remote: https://rubygems.org/
diff --git a/gemfiles/rubocop_0.27.1.gemfile.lock b/gemfiles/rubocop_0.27.1.gemfile.lock
index 15f9868..354eaf4 100644
--- a/gemfiles/rubocop_0.27.1.gemfile.lock
+++ b/gemfiles/rubocop_0.27.1.gemfile.lock
@@ -1,8 +1,8 @@
 PATH
   remote: ../
   specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
+    rubocop-checkstyle_formatter (0.2.0)
+      rubocop (>= 0.20.1)
 
 GEM
   remote: https://rubygems.org/
diff --git a/gemfiles/rubocop_0.28.0.gemfile.lock b/gemfiles/rubocop_0.28.0.gemfile.lock
index e54dcbc..6dbd2c0 100644
--- a/gemfiles/rubocop_0.28.0.gemfile.lock
+++ b/gemfiles/rubocop_0.28.0.gemfile.lock
@@ -1,8 +1,8 @@
 PATH
   remote: ../
   specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
+    rubocop-checkstyle_formatter (0.2.0)
+      rubocop (>= 0.20.1)
 
 GEM
   remote: https://rubygems.org/
diff --git a/gemfiles/rubocop_0.29.1.gemfile.lock b/gemfiles/rubocop_0.29.1.gemfile.lock
index 61a7731..c03586b 100644
--- a/gemfiles/rubocop_0.29.1.gemfile.lock
+++ b/gemfiles/rubocop_0.29.1.gemfile.lock
@@ -1,8 +1,8 @@
 PATH
   remote: ../
   specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
+    rubocop-checkstyle_formatter (0.2.0)
+      rubocop (>= 0.20.1)
 
 GEM
   remote: https://rubygems.org/
diff --git a/gemfiles/rubocop_0.30.1.gemfile.lock b/gemfiles/rubocop_0.30.1.gemfile.lock
index af6945f..33d3572 100644
--- a/gemfiles/rubocop_0.30.1.gemfile.lock
+++ b/gemfiles/rubocop_0.30.1.gemfile.lock
@@ -1,8 +1,8 @@
 PATH
   remote: ../
   specs:
-    rubocop-checkstyle_formatter (0.1.1)
-      rubocop (>= 0.14.0)
+    rubocop-checkstyle_formatter (0.2.0)
+      rubocop (>= 0.20.1)
 
 GEM
   remote: https://rubygems.org/
diff --git a/rubocop-checkstyle_formatter.gemspec b/rubocop-checkstyle_formatter.gemspec
index 714cfee..e5c750a 100644
--- a/rubocop-checkstyle_formatter.gemspec
+++ b/rubocop-checkstyle_formatter.gemspec
@@ -4,7 +4,7 @@ $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 
 Gem::Specification.new do |gem|
   gem.name          = 'rubocop-checkstyle_formatter'
-  gem.version       = '0.1.1'
+  gem.version       = '0.2.0'
   gem.authors       = ['Eito Katagiri']
   gem.email         = ['eitoball@gmail.com']
   gem.description   = %q{A formatter for rubocop that outputs in checkstyle format}
@@ -17,7 +17,7 @@ Gem::Specification.new do |gem|
   gem.test_files    = gem.files.grep(%r{^(test|spec|features)/})
   gem.require_paths = ['lib']
 
-  gem.add_dependency 'rubocop', '>= 0.14.0'
+  gem.add_dependency 'rubocop', '>= 0.20.1'
   gem.add_development_dependency 'appraisal', '~> 1.0.0'
   gem.add_development_dependency 'bundler', '~> 1.3'
   gem.add_development_dependency 'rake', '~> 10.1'