fix timestamp issue

app/message_processor.py

@@ -72,7 +72,7 @@ class MessageProcessor:
             'originalpurpose': '',
             'originalquestion': '',
             'systemresponse': '',
-            'timestamp': timestamp,
+            'timestamp': [timestamp],
             'isdone': False
         }
         conv = await loop.run_in_executor(None, lambda: sheets_client.log_conversation(**log_kwargs))