Fix relativizing directory on non-path remotes

Appraisal was creating invalid lock files, because paths weren't being
relatived correctly. e.g.:

    remote: https://github.com/thoughtbot..raisal

Instead of:

    remote: https://github.com/thoughtbot/appraisal

This PR solves this issue by replacing only the absolute paths that are
preceded by a space.

lib/appraisal/appraisal.rb

@@ -107,7 +107,10 @@ def relativize
       lockfile_content = File.read(lockfile_path)
 
       File.open(lockfile_path, 'w') do |file|
-        file.write lockfile_content.gsub(/#{current_directory}/, relative_path.to_s)
+        file.write lockfile_content.gsub(
+          / #{current_directory}/,
+          " #{relative_path}",
+        )
       end
     end
 

spec/acceptance/cli/install_spec.rb

@@ -40,6 +40,26 @@
       not_to include(current_directory)
   end
 
+  it "does not relativize directory of uris in gemfile.lock" do
+    build_gemspec
+    add_gemspec_to_gemfile
+
+    build_git_gem("uri_dummy")
+    uri_dummy_path = "#{current_directory}/uri_dummy"
+    FileUtils.symlink(File.absolute_path("tmp/gems/uri_dummy"), uri_dummy_path)
+
+    build_appraisal_file <<-APPRAISAL
+      appraise '1.0.0' do
+        gem 'uri_dummy', git: 'file://#{uri_dummy_path}'
+      end
+    APPRAISAL
+
+    run "appraisal install"
+
+    expect(content_of("gemfiles/1.0.0.gemfile.lock")).
+      to include("file://#{uri_dummy_path}")
+  end
+
   context 'with job size', :parallel => true do
     before do
       build_appraisal_file <<-Appraisal