Use correct socket type (PUB) for iopub channel
Use correct socket type (PUB) for iopub channel

Ping @ramnathv - I think this fixes your issue with no visible output,
discussed in gh-2. I saw the same issue when I compiled rzmq against ZMQ
4, and this fixed it.

mikecroucher/IRkernel,ibm-et/IRkernel,JanSchulz/IRkernel,elaOnMars/IRkernel,rgbkrk/IRkernel,chendaniely/IRkernel,ibm-et/IRkernel,gdtm86/IRkernel,ChinaQuants/IRkernel,Phobia0ptik/IRkernel