Update quick-webpack-configuration.md
Update quick-webpack-configuration.md

In webpack 2, the default for `resolve.modules` is ['node_modules'], but this is only populated if `resolve.modules` is empty in the config.  That means if you want to provide your own `resolve.modules`, you also need to add in `node_modules` to the array b/c web pack will not add it itself; i.e.: you need to add the default back in.
JeffreyWay/laravel-mix