message: webpack: include contenthash in CSS filenames
  This will bust the cache when our CSS changes.
diff: @@ -19,7 +19,7 @@ const NODE_ENV = process.env.NODE_ENV;
  const HOT_RELOAD = process.env.HOT_RELOAD;
  /* Helpers */
  -const extractCSS = new MiniCssExtractPlugin({ filename: 'app-bundle.css' });
  +const extractCSS = new MiniCssExtractPlugin({ filename: 'app-bundle.[contenthash].css' });
  const overpassTest = /overpass-.*\.(woff2?|ttf|eot|otf)(\?.*$|$)/;
  const config: Configuration = {
  