Fix webpack-dev-server compatibility

- Downgrade webpack-dev-server to 3.11.3 for webpack-cli 3.x compatibility
- Update config/dev.env.js to use named import for webpack-merge

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

config/dev.env.js

@@ -1,5 +1,5 @@
 'use strict'
-const merge = require('webpack-merge')
+const { merge } = require('webpack-merge')
 const prodEnv = require('./prod.env')
 
 module.exports = merge(prodEnv, {