Update isort pre-commit hook source repository.

The mirrors-isort respository has been deprecated per this Pull Request:
https://github.com/pre-commit/mirrors-isort/pull/13
Since isort includes pre-commit configuration in current versions we will
switch to using it directly.

.pre-commit-config.yaml

@@ -64,10 +64,10 @@ repos:
     rev: v2.1.1
     hooks:
       - id: seed-isort-config
-  - repo: https://github.com/pre-commit/mirrors-isort
+  - repo: https://github.com/timothycrosley/isort
     # pick the isort version you'd like to use from
     # https://github.com/pre-commit/mirrors-isort/releases
-    rev: v4.3.21
+    rev: 4.3.21
     hooks:
       - id: isort
   - repo: https://github.com/ansible/ansible-lint.git