TravisCI: Replace obsolete "iojs" target with Node 4.x and 5.x
TravisCI: Replace obsolete "iojs" target with Node 4.x and 5.x

givanse/broccoli-babel-transpiler,babel/broccoli-babel-transpiler,rwjblue/broccoli-babel-transpiler,kellyselden/broccoli-babel-transpiler