Hide scrollbars when not needed

<b>Before:</b>
This is how it looks at 1024px (Arrows indicate unscrollable scrollbars) : 

![jest painless javascript unit testing1](https://cloud.githubusercontent.com/assets/3154126/3219225/8d7655f6-eff3-11e3-9d28-09a1e9345b17.png)

<b>After:</b>

![jest painless javascript unit testing2](https://cloud.githubusercontent.com/assets/3154126/3219372/14942986-eff5-11e3-8366-47263c72771d.png)