Switch to official isort repository for pre-commit

.pre-commit-config.yaml

@@ -3,8 +3,8 @@ repos:
     rev: v2.1.0
     hooks:
     -   id: seed-isort-config
--   repo: https://github.com/pre-commit/mirrors-isort
-    rev: v4.3.21
+-   repo: https://github.com/timothycrosley/isort
+    rev: 4.3.21
     hooks:
     -   id: isort
 -   repo: https://github.com/ambv/black