set up nodejs version in Travis
set up nodejs version in Travis

OzTK/elm-express-typescript-webpack-boilerplate,OzTK/elm-express-boilerplate,OzTK/elm-express-boilerplate,OzTK/elm-express-typescript-webpack-boilerplate,OzTK/elm-express-boilerplate,OzTK/elm-express-typescript-webpack-boilerplate