Bump Stylus to 0.38

I'd much rather see relaxed dependency versions from #58 combined with [npm shrinkwrap](https://npmjs.org/doc/shrinkwrap.html) but I still need the [resolveURL fix](https://github.com/LearnBoost/stylus/commit/424ffbc43f6d56fed5647a99e485a7a6b5d26708) in 0.38