fix display of traffic graph

Since commit 286996b4b1d47aa073c88e1733ff4d9c3efe2020 the traffic graph has spilled out

Think I found the issue. 

Before 
![screenshot from 2014-08-25 14 21 54](https://cloud.githubusercontent.com/assets/4223752/4030334/d25af20e-2c5b-11e4-8cd9-892c78e525eb.png)

![screenshot from 2014-08-25 14 22 21](https://cloud.githubusercontent.com/assets/4223752/4030351/088efc12-2c5c-11e4-8917-654f0d9b5a93.png)