Parsing HTML with regular expressions

I've hit the bug illustrated by this failing test in which `' + generate() + '` is fed into Sass.

I'm not terribly excited about patching [this regex][regex]; what are your thoughts on using Nokogiri/[Oga][replace] here instead? How much of a concern is performance?

  [regex]: https://github.com/AndrewKvalheim/middleman/blob/429e7d64bd306c5139748ad578c47616bc4dfef2/middleman-core/lib/middleman-more/extensions/minify_css.rb#L32
  [replace]: https://github.com/middleman/middleman-blog/pull/226