Update mongo_impl.py

lightrag/kg/mongo_impl.py

@@ -1,6 +1,10 @@
 import os
 from tqdm.asyncio import tqdm as tqdm_async
 from dataclasses import dataclass
+import pipmaster as pm
+if not pm.is_installed("pymongo"):
+    pm.install("pymongo")
+
 from pymongo import MongoClient
 from typing import Union
 from lightrag.utils import logger