No Sass / Node build test

[ameliabradley]

I've considered adding a Node build test to Linfo. For now it could just do a sanity check that the Sass and JavaScript compile correctly. Later it could do more complicated things (like running eslint or JS unit tests.)

But while TravisCI has excellent support for both PHP and Node, the way the .travis.yml test matrix works we'd end up running the Node build test on every one of our PHP unit test platforms. This doesn't add much to our build time. It just seems unnecessary and inefficient.

We could use a different testing framework for the Node compilation. There's Semaphore. I don't consider it particularly ideal to have two CI platforms, but I guess GitHub supports it.

Ideally though, someone with more TravisCI experience can prove me wrong here!

Thoughts? Suggestions?