load webpack.prod.conf when NODE_ENV=production (vuejs-templates#864)

Author: helaili

template/build/dev-server.js

@@ -10,7 +10,7 @@ var path = require('path')
 var express = require('express')
 var webpack = require('webpack')
 var proxyMiddleware = require('http-proxy-middleware')
-var webpackConfig = {{#if_or unit e2e}}process.env.NODE_ENV === 'testing'
+var webpackConfig = {{#if_or unit e2e}}process.env.NODE_ENV === 'testing' || 'production'
   ? require('./webpack.prod.conf')
   : {{/if_or}}require('./webpack.dev.conf')