Fix bug with includePaths

### problem
The value of `opts.includePaths` was somehow lost between files in the stream.

### fix
Create an array called `collectedIncludePaths` that retains all values of `opts.includePaths` that pass through the stream. The `collectedIncludePaths` is passed to node-sass as the `includePaths` value.

### etc.
The indentation was off so I normalized the file to use spaces. Let me know if this makes the PR too hard to read and I'll submit one that retains the original indentation.