updated some dependencies and made SASS compilation asynchronous

I added the 'auto-inject' option from cssify, because I need it for my own purposes.
Besides that I updated the non-test dependencies (also using the newer version of cssify) and made sass compilation asynchronous 
I noticed that the tests don't pass, but they didn't in your original branch so I didn't go in more detail to find the cause. (hoping I didn't introduce bugs and that the error lies in the tests themselves).