Update to Webpack 4

[cmalven]

This generator always installs the latest version of Webpack (which is now v4) and Webpack v4 removes support for the CommonsChunkPlugin, which should be replaced with config.optimization.splitChunks.

So if you create a new project with this generator right now, you'll get an error when bundling with Webpack.

Webpack 4.0 doesn't even have documentation available yet so might be easiest to wait until that happens before trying to do anything about this.

Temporary solution if you run into this is to update your web pack version in package.json to 3.11.0 and run yarn install again.

[cmalven]

Temporary fix implemented in #144

We should keep this issue open until we've successfully migrated to 4.0

[cmalven]

So far the best source of migration info I’ve found: https://developers.google.com/web/fundamentals/performance/webpack/decrease-frontend-size