See the general upgrading guidelines here.
The 'timeout' flag has been removed from the send receive flags. In
3.1 the native zeromq sndtimeo and rcvtimeo flags where added. You
should use these instead.
Also, is in zeromq as a whole the hwm flag has been replaced with sndhwm and rcvhwm.
The rest of the things in that upgrade guide can be ignored. The erlzmq2 nif binding abstracts that away for you.