update prompt

app.py

@@ -851,7 +851,7 @@ When you have gathered all the information to provide final answer, you must use
 Thought: I now know the final answer
 Final Answer: the final answer to the original input question
 '''
-If **Thought:** or **Final Answer:** are missing in the response, please re-write the response.
+If **Thought:** or **Final Answer:** is missing in the response, please re-write the response.
 """
 
 SUFFIX = """