Switch to langchain_community (#758)

* Switch to langchain_community

PyPDFLoader was still using langhain instead of lanhchain.community, this has been replaced.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

packages/jupyter-ai/jupyter_ai/document_loaders/directory.py

@@ -5,9 +5,9 @@
 from typing import List
 
 import dask
-from langchain.document_loaders import PyPDFLoader
 from langchain.schema import Document
 from langchain.text_splitter import TextSplitter
+from langchain_community.document_loaders import PyPDFLoader
 
 
 # Uses pypdf which is used by PyPDFLoader from langchain