chore(deps): bump rexml from 3.3.7 to 3.3.9 (#247)

Author: machikoyasuda

Gemfile.lock

@@ -53,7 +53,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.11.1)
       ffi (~> 1.0)
-    rexml (3.3.7)
+    rexml (3.3.9)
     rouge (4.4.0)
     safe_yaml (1.0.5)
     sassc (2.4.0)