Fix highlighting when a string is given as a parameter to a method.

I noticed that when I passed a literal string in a method call, it would throw off the highlighting.

Before my change: 

![screen shot 2014-06-14 at 23 22 38](https://cloud.githubusercontent.com/assets/1159146/3280313/7886f0c6-f456-11e3-8355-53d9396c6a2d.png)


After my change: 

![screen shot 2014-06-14 at 23 22 09](https://cloud.githubusercontent.com/assets/1159146/3280314/7ffe4034-f456-11e3-80be-14550117ecd3.png)