Re-escape commas when updating classes

[bradlc]

Fixes #45

When running classes through postcss-selector-parser (in updateAllClasses and updateLastClasses) the classes (which we have already escaped, see #91) are re-escaped, and the commas are converted back from \2c  to \,. This PR converts them back so that commas in classes containing variants are not affected by the minifier bug.

I'm not sure if setting raws.value is the best way to do this, so open to other suggestions! Another option I considered is to run escapeCommas on the result in these functions, but result is a full selector (e.g. .something .another div) so this felt less "correct" to me.

[adamwathan]

I think this makes sense, I will dive into the raws.value thing and try and remember exactly how that works but if the tests are passing then it's at least as good as it was so worth merging! Thanks man.