Merge pull request #28 from aws-solutions-library-samples/dependabot/bundler/docs/rexml-3.3.3

Bump rexml from 3.3.0 to 3.3.3 in /docs

Author: yubingjiaocn

docs/Gemfile.lock

@@ -65,7 +65,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.11.1)
       ffi (~> 1.0)
-    rexml (3.3.0)
+    rexml (3.3.3)
       strscan
     rouge (4.3.0)
     safe_yaml (1.0.5)