Fixed valid vercel.json for Streamlit deployment

vercel.json

@@ -1,14 +1,14 @@
 {
   "version": 2,
   "builds": [
-    { "src": "index.py", "use": "@vercel/python" }
+    { "src": "app.py", "use": "@vercel/python" }
   ],
   "routes": [
-    { "src": "/(.*)", "dest": "index.py" }
+    { "src": "/(.*)", "dest": "app.py" }
   ],
   "env": {
     "STREAMLIT_SERVER_HEADLESS": "true",
     "STREAMLIT_SERVER_ENABLECORS": "false",
     "STREAMLIT_SERVER_PORT": "8000"
   }
-}
+}