[rabbitmq] March Hare 2.1.0+

[Release notes](http://blog.rubyrabbitmq.info/blog/2014/01/16/march-hare-2-dot-1-0-is-released/): nothing that may affect Logstash, though.
Merge pull request #970 from michaelklishin/patch-1

[rabbitmq] March Hare 2.1.0+