Update app.py

app.py

@@ -1,6 +1,7 @@
 from pymongo import MongoClient
 from langchain.embeddings.openai import OpenAIEmbeddings
-from langchain.vectorstores import MongoDBAtlasVectorSearch
+# error since Jan 2024, from langchain.vectorstores import MongoDBAtlasVectorSearch
+from langchain_community.vectorstores import MongoDBAtlasVectorSearch
 from langchain.document_loaders import DirectoryLoader
 from langchain.llms import OpenAI
 from langchain.chains import RetrievalQA