Update

Signed-off-by: junjie.jiang <junjie.jiang@zilliz.com>

qa_prompt.py

@@ -1,7 +1,9 @@
 from typing import List, Tuple, Dict, Optional
 
+from towhee.operator import PyOperator
 
-class QAPrompt:
+
+class QAPrompt(PyOperator):
     def __init__(self):
         super().__init__()
         self._template = """Use the following pieces of context to answer the question at the end.