Webpack 2 Support

[rhysldavis]

Really enjoying the guide. Ran into a versioning issue where the default package for webpack is now >2.0.0, this means that the initial run of npm start in Lesson 5 fails to execute with a pretty useless error message unless you downgrade to your version of webpack.

Is it possible to either a) put in a warning in lesson about webpack version, or b) update guide to handle webpack 2?