Double configuration necessary to change HMR url

[wanbinkimoon]

IMO this is confusing, while the docs suggest to edit the port forwarding in nwb.config.js this configuration will be overridden unless the same argument is specified in the command.

https://github.com/insin/nwb/blob/734537207b9024145c97c3a6c8a78366b311c705/src/createServerWebpackConfig.js#L26

To override the default configuration I had both to define a nwb.config.js

module.exports = {
  type: 'react-app', 
  devServer: {
    port: 3000,
    public: "localhost:3000",
    publicPath: "http://localhost:3000/", 
    disableHostCheck: true,
    open: false
  },
  webpack: {
    publicPath: "http://localhost:3000/", 
  }
}

and define the port in the command in package.json

{
...
scripts: {
  ...
  "start": "nwb serve-react-app --port 3000",
}

[insin]

This is similar to #524, as any args config will have been added to serverConfig by this point, so it should only be checking serverConfig at this point - I should be able to fix both at the same time.