Merge pull request #401 from treefrogframework/dependabot/bundler/docs/rexml-3.3.6

Bump rexml from 3.2.8 to 3.3.6 in /docs

Author: treefrogframework

docs/Gemfile.lock

@@ -240,8 +240,8 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rexml (3.2.8)
-      strscan (>= 3.0.9)
+    rexml (3.3.6)
+      strscan
     rouge (3.30.0)
     ruby2_keywords (0.0.5)
     rubyzip (2.3.2)