Bump rexml from 3.3.4 to 3.3.6 (#440)

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.4 to 3.3.6.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.3.4...v3.3.6)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -61,7 +61,7 @@ GEM
     rdiscount (2.2.7.3)
     rerun (0.14.0)
       listen (~> 3.0)
-    rexml (3.3.4)
+    rexml (3.3.6)
       strscan
     ruby2_keywords (0.0.5)
     sinatra (4.0.0)