Bump rexml from 3.3.9 to 3.4.2 (#60)

Author: dependabot[bot]

Gemfile.lock

@@ -85,7 +85,7 @@ GEM
     netrc (0.11.0)
     nkf (0.2.0)
     public_suffix (4.0.7)
-    rexml (3.3.9)
+    rexml (3.4.2)
     ruby-macho (2.5.1)
     securerandom (0.3.1)
     typhoeus (1.4.1)