Update app.py

fixed an error (max_token => max_tokens)

app.py

@@ -14,7 +14,7 @@ def respond(message, history):
     
     messages.append({"role": "user", "content": message})
 
-    response = client.chat_completion(messages, max_token = 100)
+    response = client.chat_completion(messages, max_tokens = 100)
             
     return response['choices'][0]['message']['content'].strip()