Update app.py

app.py

@@ -78,7 +78,7 @@ def respond(
     query_str = message
     response = query_engine.query(query_str)
     #
-    return response
+    return str(response)
 #
 """
 For information on how to customize the ChatInterface, peruse the gradio docs: https://www.gradio.app/docs/chatinterface