[pre-commit.ci] pre-commit autoupdate (#644)

updates:
- [github.com/psf/black: 20.8b1 → 21.4b2](psf/black@20.8b1...21.4b2)
- [github.com/PyCQA/flake8: 3.9.0 → 3.9.1](PyCQA/flake8@3.9.0...3.9.1)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: pre-commit-ci[bot]

.pre-commit-config.yaml

@@ -13,7 +13,7 @@ repos:
   - id: end-of-file-fixer
   - id: trailing-whitespace
 - repo: https://github.com/psf/black
-  rev: 20.8b1
+  rev: 21.4b2
   hooks:
   - id: black
     language_version: python3
@@ -22,7 +22,7 @@ repos:
   hooks:
   - id: isort
 - repo: https://github.com/PyCQA/flake8
-  rev: 3.9.0
+  rev: 3.9.1
   hooks:
   - id: flake8
     additional_dependencies: