Bump rexml from 3.2.9 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.9 to 3.3.9.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.2.9...v3.3.9)

---
updated-dependencies:
- dependency-name: rexml
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -299,8 +299,7 @@ GEM
     regexp_parser (2.8.0)
     reline (0.5.8)
       io-console (~> 0.5)
-    rexml (3.2.9)
-      strscan
+    rexml (3.3.9)
     rspec-core (3.12.2)
       rspec-support (~> 3.12.0)
     rspec-expectations (3.12.3)
@@ -361,7 +360,6 @@ GEM
     sqlite3 (1.6.2-x86_64-darwin)
     sqlite3 (1.6.2-x86_64-linux)
     stringio (3.1.0)
-    strscan (3.1.0)
     swd (1.3.0)
       activesupport (>= 3)
       attr_required (>= 0.0.5)