postcss-loader requires sourceMap option

[hsimah]

I'm still new to node, webpack and this whole brave new world of js development. Your ampersand.js/react tutorial really helped me get started.

I upgraded all my packages to newish versions and received a warning from postcss-loader regarding the source mapping. Turns out there is a sourceMap boolean option that is required. I have manually added it in in installed-style-loaders.js and the warning goes away. I don't feel comfortable creating a PR for this as I don't quite know the ramifications.

[selbekk]

Thanks for your feedback @hsimah! Actually, we'd love you to create a PR for us - and we'll do the testing and releasing of a patched version. =)