Update app.py

app.py

@@ -45,7 +45,7 @@ session_id = uuid4()
 # deprecated (llama-index 0.9)
 storage_context = StorageContext.from_defaults(persist_dir='./')
 # gpt-3.5-turbo is the current default model
-llm = OpenAI(temperature=0.5, model="gpt-4")
+llm = OpenAI(temperature=0.5, model_name="gpt-4")
 service_context = ServiceContext.from_defaults(llm=llm)
 index = load_index_from_storage(storage_context, service_context=service_context)
 # for llama-index 0.10