In reference to the issue #9 , I found a boolean setting for webpack-dev-server which enables writing the changed files to disk. You just need to add writeToDisk: true to the devServer part in webpack.dev.js:

  devServer: {
    contentBase: [
      path.resolve('_site'),
    ],
    hot: true,
    writeToDisk: true,
  },

The docs for the relevant option is here: https://webpack.js.org/configuration/dev-server/#devserverwritetodisk-