Making it so that (dev) is not added to the manifest.json for permissions

Chrome does not recognize permissions with (dev) on the end, so remove them.
![image](https://cloud.githubusercontent.com/assets/2047962/4311244/1e749466-3ead-11e4-9d16-9fb9b42acc3f.png)

why not `.replace(' (dev)', '')` rather than a complicated logic with substring?