change autoprefixer transform to be able to understand multiple conditions

buildProduction takes an option --autoprefix which is a string that defines the rules.

It was not possible to give more than one condition to autoprefixer because it doesn't understand a string with comma seperated values as input, and because the input string was wrapped in a list.

Now the input string is split on /,\s*/ and fed to autoprefixer as a list of individual conditions.