fix: vercel playground build error

Author: zcf0508

packages/playground/package.json

@@ -4,6 +4,7 @@
   "private": true,
   "scripts": {
     "dev": "nuxt dev",
+    "build": "nuxt build",
     "start": "cross-env PORT=3003 node .output/server/index.mjs"
   },
   "dependencies": {