Bump rexml from 3.4.1 to 3.4.2 in /docs

Bumps [rexml](https://github.com/ruby/rexml) from 3.4.1 to 3.4.2. - [Release notes](https://github.com/ruby/rexml/releases) - [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md) - [Commits](ruby/rexml@v3.4.1...v3.4.2) --- updated-dependencies: - dependency-name: rexml dependency-version: 3.4.2 dependency-type: indirect ... Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/Gemfile.lock

@@ -100,7 +100,7 @@ GEM
  rb-fsevent (0.11.2)
  rb-inotify (0.11.1)
  ffi (~> 1.0)
- rexml (3.4.1)
+ rexml (3.4.2)
  rouge (4.5.2)
  safe_yaml (1.0.5)
  sass-embedded (1.89.2)