Do not send RDY re-ups now that NSQ 0.3.0 doesn't require this

See this change for 0.3.0: https://github.com/bitly/nsq/blob/master/ChangeLog.md#030---2014-11-18
Because of this, we no longer need to send RDY back to the server when we want more messages. This means we have slightly less communication over the wire and even simpler client code.

The problem with this change is it breaks this library for all version of NSQ < 0.3.0. What should we do?!