Using "vm" for "ViewModel" to remain consistent.

As mentioned [here](https://github.com/toddmotto/angularjs-styleguide/commit/47a125d71c50a56515c7b4aadcd31247d74dc723#commitcomment-7627650)
Merge pull request #16 from kentcdodds/patch-1

Using "vm" for "ViewModel" to remain consistent.