Change qa threshold from a constant to lower bound var.

Chatbot/chatbot.py

@@ -115,7 +115,7 @@ def listen(self, sentence, target=None, api_key=None, qa_threshold=35, qa_block_
         # Assume that there are no intent in the sentence, consider this questions
         # is qa again, but this time use a smaller threshold.
         else:
-            if qa_sim > 60:
+            if qa_sim > qa_threshold:
                 return qa_response,None,None,None
             else:
                 # This query has too low similarity for all matching methods.