Update app.py

app.py

@@ -4,7 +4,7 @@ from PyPDF2 import PdfReader
 from langchain_text_splitters import RecursiveCharacterTextSplitter
 from langchain_community.vectorstores import FAISS
 from langchain_community.embeddings import HuggingFaceEmbeddings
-from langchain_community.chains import RetrievalQA
+from langchain.chains.retrieval_qa.base import RetrievalQA
 from langchain.prompts import PromptTemplate
 from langchain_core.language_models.llms import LLM
 from langchain_core.callbacks import CallbackManagerForLLMRun