update: 代码优化

build/webpack.prod.conf.js

@@ -32,7 +32,8 @@ var webpackConfig = merge(baseWebpackConfig, {
   plugins: [
     // http://vuejs.github.io/vue-loader/en/workflow/production.html
     new webpack.DefinePlugin({
-      'process.env': env
+      'process.env': env,
+      'process.env.PACK_ENV': JSON.stringify(process.env.PACK_ENV)
     }),
     new webpack.optimize.UglifyJsPlugin({
       compress: {