fix(windows): Fixes path seperator on windows.

Theres a bug on windows whereby expanding a path defined like `/test.css.styl` will expand to `/test.css` and the styl file won't be found. This is due to the hardcoding of the path separator.
Also fixed a missing semicolon that was failing jslint.

Originally opened an issue in mincer repo until I looked into it a bit more. https://github.com/nodeca/mincer/issues/165