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

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

Author: pre-commit-ci[bot]

nbviewer/tests/test_json.py

@@ -1,9 +1,9 @@
 import json
 import os
+from typing import Optional
 from unittest import TestCase
 
 from jsonschema import validate
-from typing import Optional
 
 
 ROOT = os.path.abspath(os.path.join(os.path.dirname(__file__), "..", ".."))