pre-commit: Update some hooks (Chia-Network#8309)

* pre-commit: Update `flake8` to 3.9.2

* pre-commit: Update `pre-commit-hooks` to 4.0.1

* pre-commit: Update `black` to 21.8b0

.pre-commit-config.yaml

@@ -1,6 +1,6 @@
 repos:
 -   repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v2.3.0
+    rev: v4.0.1
     hooks:
     -   id: check-yaml
     -   id: end-of-file-fixer
@@ -10,11 +10,11 @@ repos:
     -   id: check-ast
     -   id: debug-statements
 -   repo: https://github.com/psf/black
-    rev: 21.6b0
+    rev: 21.8b0
     hooks:
     -   id: black
 -   repo: https://gitlab.com/pycqa/flake8
-    rev: 3.7.9
+    rev: 3.9.2
     hooks:
     - id: flake8
 -   repo: https://github.com/pre-commit/mirrors-mypy