Switch from zmq to zeromq to avoid compilation

It seems the [zmq](https://www.npmjs.com/package/zmq) package needs to compile ZeroMQ from source which is a problem if you do not have the compilation toolchain installed. I was able to switch to the [zeromq](http://zeromq.github.io/zeromq.js/) package which comes with pre-built binaries and saves you the step of having to install g++.