Bump rexml from 3.3.4 to 3.3.6 (#61)

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

@@ -45,7 +45,7 @@ GEM
       ruby-progressbar
     public_suffix (6.0.1)
     rake (13.2.1)
-    rexml (3.3.4)
+    rexml (3.3.6)
       strscan
     ruby-progressbar (1.13.0)
     simplecov (0.22.0)