Fix highlighted line

Hi,

This is a fix for https://github.com/chriskempson/base16-textmate/issues/12
Screenshot:
![dark_highlight](https://f.cloud.github.com/assets/752030/962564/33e64150-04f2-11e3-81e1-fa2b88379c88.png)
![light_highlight](https://f.cloud.github.com/assets/752030/962565/33f4dee0-04f2-11e3-9f2c-3115ae364fd3.png)