Setup Travis about edx-lint

[nedbat]

I would like to divide this repo into the three separate repos it should be, rather than push this one to PyPI.

[clintonb]

@nedbat do you have an ETA for that work?

[nedbat]

I don't, it's all spare-time work. I guess it isn't a disaster to push the three-headed beast to PyPI, we can push the proper repos later when we have them.

[clintonb]

@nedbat I'm fine holding off on PyPI. I at least want to run tests. I prefer "build passed on Travis" to "It works on my machine".