re-add next export command

Author: jpdriver

demo/package.json

@@ -7,7 +7,7 @@
     "prebuild": "cd .. && yarn && yarn build",
     "prebuild:npm": "cd .. && npm i && npm run build",
     "dev": "next dev",
-    "build": "next build",
+    "build": "next build && next export",
     "start": "next start"
   },
   "dependencies": {