Enable Source Maps

[martynchamberlin]

The ability to set up break points is important, and currently, it's not possible in this plugin, using the source files.

This line isn't working.

[martynchamberlin]

Also, why are we returning an array here instead of an object? There's no reason that I can see for this. There's complexity here that is unwarranted. This should just be a straight forward webpack config file. The only thing special about this is that we change the output file based on whether you're FireFox or Chrome. That's it.