Update app.py

Corrected to : from langchain_community.chains import RetrievalQA

app.py

@@ -12,7 +12,7 @@ from langchain_huggingface import HuggingFaceEndpoint
 from langchain_text_splitters import RecursiveCharacterTextSplitter
 from langchain_community.vectorstores import Chroma
 from langchain_community.document_loaders import PyPDFLoader
-from langchain.chains import RetrievalQA
+from langchain_community.chains import RetrievalQA
 #from huggingface_hub import HfFolder
 from langchain_community.embeddings import HuggingFaceEmbeddings
 from huggingface_hub import InferenceClient