update app.py

app.py

@@ -6,7 +6,7 @@ from datetime import datetime
 from dotenv import load_dotenv
 from langchain_openai import OpenAIEmbeddings, ChatOpenAI
 from langchain_community.vectorstores import FAISS
-from langchain_classic.chains import RetrievalQA
+from langchain.chains import RetrievalQA
 from langchain_core.prompts import PromptTemplate
 
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