added rgba-hex plugin
added rgba-hex plugin

postcss/postcss,jedmao/postcss,XOP/postcss,maximkoretskiy/postcss,jonathantneal/postcss,dehuszar/postcss,Semigradsky/postcss,andrepolischuk/postcss,alanev/postcss,postcss/postcss,bezoerb/postcss,pascalduez/postcss