[pre-commit.ci] pre-commit autoupdate (#115)

updates:
- [github.com/psf/black: 21.7b0 → 21.8b0](psf/black@21.7b0...21.8b0)

Co-authored-by: Chris Sewell <chrisj_sewell@hotmail.com>

Author: pre-commit-ci[bot]

.pre-commit-config.yaml

@@ -51,7 +51,7 @@ repos:
       args: [--py37-plus]
 
   - repo: https://github.com/psf/black
-    rev: 21.7b0
+    rev: 21.8b0
     hooks:
     - id: black