Merge branch 'update-rouge-gemfile-lock' into 'master'

Update Gemfile.lock with rouge 3.15.0

See merge request gitlab-org/gitlab!23375

Gemfile.lock

@@ -1328,7 +1328,7 @@ DEPENDENCIES
   request_store (~> 1.3)
   responders (~> 3.0)
   retriable (~> 3.1.2)
-  rouge (~> 3.11.0)
+  rouge (~> 3.15.0)
   rqrcode-rails3 (~> 0.1.7)
   rspec-parameterized
   rspec-rails (~> 4.0.0.beta3)