Fixes nav buttons alignment issue

Closes #620 

Tested on iOS simulator. 

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![image](https://cloud.githubusercontent.com/assets/302258/3772220/d5171274-18fc-11e4-99bc-8436999ae4eb.png)
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![image](https://cloud.githubusercontent.com/assets/302258/3772233/f49848d4-18fc-11e4-8725-ed31d96e5309.png)