Setup Travis-CI build server

[kylepjohnson]

This was hanging, too, like the RTD build. I haven't been able to confirm that the caching actually worked for the stanford models. This would be a big help for speed.

This method might cause hangs, too, and could perhaps be removed for now: https://github.com/cltk/cltkv1/blob/master/src/cltkv1/wrappers/stanford.py#L202

after_success should push to PyPI. I can help with credentials when this is worked on.

[kylepjohnson]

@free-variation you've got things building now. We can open another issue for the final devops handoff when we're closer to prod.