fixed wrong json call

app.py

@@ -43,7 +43,7 @@ with gr.Blocks() as iface:
             message_history.append({"role": "user", "content": pair[0]})
             print()
             if pair[1] is not None:
-                message_history.append({"assistant": "user", "content": pair[1]})
+                message_history.append({"role": "assistant", "content": pair[1]})
         completion = openai.ChatCompletion.create(
             model="gpt-3.5-turbo",
             messages=message_history