add vercel config

index.js

@@ -0,0 +1 @@
+require('./app.js')

vercel.json

@@ -0,0 +1,15 @@
+{
+  "version": 2,
+  "builds": [
+    {
+      "src": "./index.js",
+      "use": "@vercel/node"
+    }
+  ],
+  "routes": [
+    {
+      "src": "/(.*)",
+      "dest": "/"
+    }
+  ]
+}