Set up an end-to-end test

[gaearon]

This is boring but needed.

Write a script we can run on Travis that tests that create-react-app something && cd something && npm run build produces a build without error in the build folder, and that npm run eject (aka "graduate" before #9 is fixed) changes the project in a way that npm run build also works.

[vjeux]

I'd love to have a dummy test that ensures that npm start does not instant fatal as well

[vjeux]

Test is here: d3f9305

Next step: hooking it up to travis

[vjeux]

Travis is not setup for facebookincubator repo yet. I'll ping the relevant people tomorrow (outside of the weekend). In the meantime this should work (tm) https://github.com/facebookincubator/create-react-app/blob/master/.travis.yml

[vjeux]

Travis is working :)))

https://travis-ci.com/facebookincubator/create-react-app/builds/28471455