Update to have json filter in core.  Added new gelfify spec test to contrib.
This is erroneously still in contrib (it's officially in core).
Merge branch 'master' of https://github.com/untergeek/logstash-contrib

* 'master' of https://github.com/untergeek/logstash-contrib:
  This is erroneously still in contrib (it's officially in core).
  Update to have json filter in core.  Added new gelfify spec test to contrib.