Add mocha to generated bower.json.

Right now to use (non ember-cli), you need to:
* `bower install --save-dev ember-mocha`
* `bower install --save-dev mocha`

Seems like this library requires `mocha` so we should just add it to our generated `bower.json`.
Merge pull request #7 from rwjblue/depend-on-mocha

Add mocha to generated bower.json.