docs: fix migration guide (#3699)

Author: yoyo837

migration-v4.md

@@ -573,7 +573,7 @@ module.exports = {
 
   ```js
   const devServerOptions = { host: "127.0.0.1", port: 8080 };
-  const devServer = new Server(compiler, devServerOptions);
+  const devServer = new Server(devServerOptions, compiler);
 
   (async () => {
     await devServer.start();