keyframes regex less greedy on minified css

Been banging my head against a wall for a while here on production!  Thought I was running into all the cross domain issues, but turns out it was the minifier all along :frowning:

@scottjehl -- Not sure how or when to write tests for this, but happy to come back and revisit if they're required for the merge.  Would love a version bump to help bower install the update (not a semver pro, but probably 1.5.0 if you're messing that deeply with the regex).

Great project and thanks for everything to date <3

-Tom