Remove borders from navbar

From
![image](https://cloud.githubusercontent.com/assets/1341236/3642220/ca65813a-10be-11e4-89e1-6e97cff53f0e.png)

To
![image](https://cloud.githubusercontent.com/assets/1341236/3642229/f9218046-10be-11e4-8769-32fdace72aa5.png)