Update messenger.mex for ubuntu.

[isbadawi]

Compiled against latest octave. Should hopefully fix the Travis build.

[isbadawi]

Seems I compiled against the wrong version of zmq. I'll try this again...

[isbadawi]

Third time's the charm...

This fixes the octave failure, now there is an error about import IPython.nbformat.v4 as nbformat which I guess is what #213 is trying to fix. I'll merge this one.

This is good for the travis build, but I'm not sure what the right thing to do is here for users. Do we need different versions of messenger.mex for different octave versions, as well as different zmq versions?

[arokem]

Thanks so much for jumping in with this @isbadawi! And apologies for being AWOL last few weeks.

[arokem]

Concerning the generally right thing to do: I think that we should go with support for recent versions of Octave and zmq. It's a stretch to support every possible combination. I have had trouble compiling the messenger against newer octave on my mac so far, but will keep trying...