Uses git function to find .git directory.


![screen shot 2014-07-04 at 8 44 42 am](https://cloud.githubusercontent.com/assets/2591516/3483634/90dd412a-0392-11e4-85b0-dfc463c5b710.png)

This should be less error prone than our current code

![pear2](https://cloud.githubusercontent.com/assets/2591516/3483645/c6f692fc-0392-11e4-8d30-a224d85f2e4c.gif)

Not sure how I feel about this...essentially we're now saying

`git rev-parse --show-toplevel` / `git rev-parse --git-dir`

I understand it's better to use git's function rather than hardcode `.git`, but I'm preeeeeeeeeeettty sure we don't need that first part?
![screen shot 2014-07-04 at 10 07 52 am](https://cloud.githubusercontent.com/assets/3118416/3484017/c40f0b1e-039c-11e4-8266-8654bb3e92e0.png)