app.py: Update to gpt-4 model

app.py

@@ -24,7 +24,7 @@ system = ("Act like you are a chatbot. Be precise and unique with your answers."
 def chatbot(prompt, temperature = 0.2, developer_mode = False):
     system_message = developer_msg if developer_mode else system
     response = opai.ChatCompletion.create(
-        model = "gpt-3.5-turbo",
+        model = "gpt-4",
         max_tokens = 1024,
         temperature = temperature,
         frequency_penalty = 0,