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

@@ -211,15 +211,11 @@ GEM
       rb-inotify (~> 0.9, >= 0.9.10)
     logger (1.6.6)
     mercenary (0.3.6)
-    mini_portile2 (2.8.8)
     minima (2.5.1)
       jekyll (>= 3.5, < 5.0)
       jekyll-feed (~> 0.9)
       jekyll-seo-tag (~> 2.1)
     minitest (5.25.5)
-    nokogiri (1.15.7)
-      mini_portile2 (~> 2.8.2)
-      racc (~> 1.4)
     nokogiri (1.15.7-x86_64-darwin)
       racc (~> 1.4)
     nokogiri (1.15.7-x86_64-linux)
@@ -234,7 +230,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.11.1)
       ffi (~> 1.0)
-    rexml (3.4.1)
+    rexml (3.4.2)
     rouge (3.30.0)
     ruby2_keywords (0.0.5)
     rubyzip (2.4.1)