Add lighter purple for file names in helm-grep.

The default purple used by `helm` for showing files during a `grep` operation are pretty dark. It's difficult to read using the `moe-dark-theme`.

For comparison, here is before the change:

![moe-dark-original-purple](https://f.cloud.github.com/assets/159257/2181035/aa2e4ad0-973f-11e3-910e-e6d72ea9964b.png)

Here is after:

![moe-dark-lighter-purple](https://f.cloud.github.com/assets/159257/2181036/b1bbfedc-973f-11e3-8848-7068220bc13b.png)