Add latest 4 node.js release to Travis CI
Add latest 4 node.js release to Travis CI

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