Update Mocha to 2.1.0

Hey, Mocha 2.1.0 features this [small fix](https://github.com/mochajs/mocha/commit/221e0360e23a41e4b8583a22a7a5f3a3aa5f55cb) that restores the ability to click the name of a test to run it individually, which obviates the minor-but-persistent hassle of re-adding “tests” to the beginning of the pathname when I need to focus on a test.

I was specifying 2.1.0 in `bower.json` and that worked okay locally, but Heroku and Travis builds were failing, so I figured I’d make this fork.

This update might not be useful for everyone, feel free to close if it seems unnecessary.