Use bless v4.0

The current version (v3.0.3) takes a significant amount of time on very large css files in terms of file size. His 4.0 branch is faster. I'm having bless pointed at my fork's dev branch instead since there are a few changes that were needed in order for 4.0 to work with our css.
I didn't want to publish the author's work on v4. He's also been very sporadic with his work on the update.

All his work has also been on a Dev branch for the past year