Fix/langchain document schema (#2539)

Co-authored-by: jyong <jyong@dify.ai>

api/core/rag/extractor/notion_extractor.py

@@ -5,9 +5,9 @@ from typing import Any, Optional
 import requests
 from flask import current_app
 from flask_login import current_user
-from langchain.schema import Document
 
 from core.rag.extractor.extractor_base import BaseExtractor
+from core.rag.models.document import Document
 from extensions.ext_database import db
 from models.dataset import Document as DocumentModel
 from models.source import DataSourceBinding