Update app.py

Added an a new import

app.py

@@ -3,6 +3,8 @@ import os
 from typing import Optional, Tuple
 
 import gradio as gr
+from langchain import PromptTemplate, HuggingFaceHub, LLMChain
+from langchain.memory import ConversationBufferWindowMemory
 from langchain.chains import ConversationChain
 from langchain.llms import OpenAI
 import random