Update app.py

app.py

@@ -161,7 +161,7 @@ def predict(input,
         VECTOR_SEARCH_TOP_K=VECTOR_SEARCH_TOP_K,
         web_content=web_content,
         chat_history=history,
-        history_len=history_len,
+        history_len=HISTORY_LEN,
         temperature=temperature,
         top_p=top_p,
     )