Fix syntax highlighting when there is a method call in string interpolation

Before change:

![screen shot 2014-06-16 at 00 28 17](https://cloud.githubusercontent.com/assets/1159146/3284274/90cdadbe-f528-11e3-8c1e-489ff359cec2.png)

After change: 

![screen shot 2014-06-16 at 00 34 04](https://cloud.githubusercontent.com/assets/1159146/3284279/a23b88be-f528-11e3-8bbb-2dbca21fc897.png)

I tried getting the parens to also highlight in white but I'm not sure how to get that :(