[auto-link-css] Added a feature to cover the nested css case

I thought this was already in.. must've backed it out.
[travis-ci] Stop trying to support 2.1.0

I develop in 2.1.0 locally.. but something's up with travis-ci.

A few weeks ago, builds were working fine with 2.1.0.. but now I can't
install.

It's not important for now.. Will try again later.