Silence webpack warning by setting mode to production

webpack.config.js

@@ -9,6 +9,7 @@ const CopyWebpackPlugin = require("copy-webpack-plugin");
 module.exports = {
     context: path.resolve(__dirname, 'src'),
     entry: './main.js',
+    mode: 'production',
     output: {
         path: path.resolve(__dirname, 'build'),
     },