Bump rexml from 3.4.0 to 3.4.2 (#60)

Author: dependabot[bot]

Gemfile.lock

@@ -142,7 +142,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.11.1)
       ffi (~> 1.0)
-    rexml (3.4.0)
+    rexml (3.4.2)
     rouge (4.5.1)
     ruby-rc4 (0.1.5)
     safe_yaml (1.0.5)