Define NODE_ENV for production build

webpack/plugins/index.ts

@@ -1,3 +1,5 @@
+import * as webpack from 'webpack';
+
 import consts from './consts';
 import hoist from './hoist';
 import minify from './minify';
@@ -7,7 +9,12 @@ const isProduction = env === 'production';
 
 export default (version, lang) => {
 	const plugins = [
-		consts(lang)
+		consts(lang),
+		new webpack.DefinePlugin({
+			'process.env': {
+				NODE_ENV: JSON.stringify(process.env.NODE_ENV)
+			}
+		})
 	];
 
 	if (isProduction) {