[pre-commit.ci] pre-commit autoupdate (#686)

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

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

.pre-commit-config.yaml

@@ -1,6 +1,6 @@
 repos:
   - repo: https://github.com/psf/black
-    rev: 21.8b0
+    rev: 21.9b0
     hooks:
       - id: black
         args: ["--target-version=py36"]