Add uglifyjs plugin (#2070)

* Add uglifyjs plugin and replace -p flag with --env.production
* Add uglifyjs plugin
* Configure UglifyJsPlugin to drop console and prevent eslint error
* Turn off no-console rule because uglifyjs plugin drops it in prod

resources/assets/build/webpack.config.optimize.js

@@ -2,6 +2,7 @@
 
 const { default: ImageminPlugin } = require('imagemin-webpack-plugin');
 const imageminMozjpeg = require('imagemin-mozjpeg');
+const UglifyJsPlugin = require('uglifyjs-webpack-plugin')
 
 const config = require('./config');
 
@@ -21,5 +22,14 @@ module.exports = {
       plugins: [imageminMozjpeg({ quality: 75 })],
       disable: (config.enabled.watcher),
     }),
+    new UglifyJsPlugin({
+      uglifyOptions: {
+        ecma: 8,
+        compress: {
+          warnings: true,
+          drop_console: true,
+        },
+      },
+    }),
   ],
 };