Add OSX builds to .travis.yml

[eugenevinitsky]

We need to test that things pass on OSX as well.

Look at ray's travis.yml for an example of how to do so.

[AboudyKreidieh]

after looking into this (and trying it), it turns out that this is not a good idea. See: travis-ci/travis-ci#7304

My recommendation is we do not do this.

[eugenevinitsky]

@AboudyKreidieh perhaps we can turn this into a slow test? I will talk to the Ray team; they do this.

[eugenevinitsky]

@AboudyKreidieh can you detail the issue you hit when you tried this? I want to see if we can build tests for our setup instructions since this is something we really struggle with

[eugenevinitsky]

Currently blocked by discussion with Travis team

[AboudyKreidieh]

This doesn't look like it will work out. Fortunately most of us use Macs, so we should be able to keep up with the build like that.