(refactor) Reduce button corner radius.

<h5>Before:</h5>
![screen shot 2014-11-15 at 4 03 42 pm](https://cloud.githubusercontent.com/assets/8163408/5059801/2682e48e-6ce1-11e4-9f5e-24fbee3aa3bd.png)

<h5>After:</h5>
![screen shot 2014-11-15 at 4 02 49 pm](https://cloud.githubusercontent.com/assets/8163408/5059799/1e1cd804-6ce1-11e4-9e4c-47a84dd79c7c.png)