Fix to work with custom $interpolationProvider

This fixes the issue found here: https://github.com/Yappli/angular-css-injector/issues/18

Simply replaced the hard-coded interpolation symbols {{ and }} with the dynamic $interpolationProvider.startSymbol() and $interpolationProvider.endSymbol().

I updated minified version of library, but it's probably not ideal. I was unsure what was previously used.

ebn