Bump rexml from 3.3.9 to 3.4.2 in /docs (#3107)

* Bump rexml from 3.3.9 to 3.4.2 in /docs

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.9 to 3.4.2.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](https://github.com/ruby/rexml/compare/v3.3.9...v3.4.2)

---
updated-dependencies:
- dependency-name: rexml
  dependency-version: 3.4.2
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

* Bump rexml from 3.3.9 to 3.4.2 in root

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Samuel Young <samuel.young@softwire.com>

Gemfile.lock

@@ -411,7 +411,7 @@ GEM
     responders (3.1.1)
       actionpack (>= 5.2)
       railties (>= 5.2)
-    rexml (3.3.9)
+    rexml (3.4.4)
     roo (2.10.1)
       nokogiri (~> 1)
       rubyzip (>= 1.3.0, < 3.0.0)

docs/Gemfile.lock

@@ -226,7 +226,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rexml (3.3.9)
+    rexml (3.4.2)
     rouge (3.26.0)
     ruby2_keywords (0.0.5)
     rubyzip (2.3.2)