docs: add missing comma to comment (#49)

Author: krfisc88

README.md

@@ -47,7 +47,7 @@ module.exports = {
     minimize: true,
     minimizer: [
       // For webpack@5 you can use the `...` syntax to extend existing minimizers (i.e. `terser-webpack-plugin`), uncomment the next line
-      // `...`
+      // `...`,
       new CssMinimizerPlugin(),
     ],
   },