now uses langchain again

app.py

@@ -1,7 +1,7 @@
 import chainlit as cl
 from chainlit.playground.providers import ChatOpenAI
 from dotenv import load_dotenv
-from langchain_community.document_loaders import PyMuPDFLoader
+from langchain.document_loaders import PyMuPDFLoader
 from langchain.text_splitter import RecursiveCharacterTextSplitter
 import tiktoken
 from langchain.prompts import ChatPromptTemplate