Merge pull request #421 from treefrogframework/dependabot/bundler/docs/rexml-3.4.2

Bump rexml from 3.3.9 to 3.4.2 in /docs

Author: treefrogframework

docs/Gemfile.lock

@@ -240,7 +240,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rexml (3.3.9)
+    rexml (3.4.2)
     rouge (3.30.0)
     ruby2_keywords (0.0.5)
     rubyzip (2.3.2)