Fixed river segment label from breaking out of box on mobile

Before the fix:

![label-broken](https://cloud.githubusercontent.com/assets/76278/4636439/c2bddace-53e2-11e4-9291-29ce451e83c6.png)

After the fix:

![label-fixed](https://cloud.githubusercontent.com/assets/76278/4636442/c6420756-53e2-11e4-9bea-98e985658419.png)