[pre-commit.ci] pre-commit autoupdate

updates:
- [github.com/psf/black: 21.8b0 → 21.9b0](psf/black@21.8b0...21.9b0)
- [github.com/PyCQA/flake8: 3.9.2 → 4.0.1](PyCQA/flake8@3.9.2...4.0.1)

.pre-commit-config.yaml

@@ -34,7 +34,7 @@ repos:
   - id: isort
 
 - repo: https://github.com/psf/black
-  rev: 21.8b0
+  rev: 21.9b0
   hooks:
   - id: black
     language_version: python3
@@ -46,7 +46,7 @@ repos:
     additional_dependencies: [black]
 
 - repo: https://github.com/PyCQA/flake8
-  rev: 3.9.2
+  rev: 4.0.1
   hooks:
   - id: flake8
     additional_dependencies: [flake8-bugbear]