dev: add gulp script

package.json

 {
   "name": "god-template",
   "scripts": {
+    "scripts:build": "node scripts/index",
     "start:analyze": "ANALYZE=1 umi dev",
     "start": "umi dev",
     "build": "umi build",
@@ -32,5 +33,8 @@
     "react-dom": "^16.12.0",
     "umi": "^3.2.0",
     "yorkie": "^2.0.0"
+  },
+  "devDependencies": {
+    "gulp": "^4.0.2"
   }
 }