Update app.py

app.py

@@ -8,6 +8,7 @@ from langchain.text_splitter import CharacterTextSplitter
 from langchain.vectorstores import FAISS
 from langchain.vectorstores import Chroma
 from langchain.chains import ConversationalRetrievalChain
+from langchain.memory import ConversationBufferMemory
 import gradio as gr
 import openai
 from langchain import PromptTemplate, OpenAI, LLMChain