Version of zeromq lib to run ezmq_zmq2_SUITE

This is to precise the dependency to run ezmq_zmq2_SUITE tests
The master branch of erlzmq2(ZeroMQ in the 3.x) is not working with ezmq_zmq2_SUITE.erl
The ezmq_zmq2_SUITE.erl only work with ZeroMQ 2.x
Merge pull request #15 from plemanach/patch-1

Version of zeromq lib to run ezmq_zmq2_SUITE