Fix linting

lightrag/kg/chroma_impl.py

@@ -1,4 +1,3 @@
-import os
 import asyncio
 from dataclasses import dataclass
 from typing import Union
@@ -20,7 +19,9 @@ class ChromaVectorDBStorage(BaseVectorStorage):
             config = self.global_config.get("vector_db_storage_cls_kwargs", {})
             cosine_threshold = config.get("cosine_better_than_threshold")
             if cosine_threshold is None:
-                raise ValueError("cosine_better_than_threshold must be specified in vector_db_storage_cls_kwargs")
+                raise ValueError(
+                    "cosine_better_than_threshold must be specified in vector_db_storage_cls_kwargs"
+                )
             self.cosine_better_than_threshold = cosine_threshold
 
             user_collection_settings = config.get("collection_settings", {})