[pre-commit.ci] pre-commit autoupdate (#684)

updates:
- [github.com/psf/black: 21.7b0 → 21.8b0](psf/black@21.7b0...21.8b0)
- [github.com/asottile/blacken-docs: v1.10.0 → v1.11.0](adamchainz/blacken-docs@v1.10.0...v1.11.0)

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

.pre-commit-config.yaml

@@ -1,12 +1,12 @@
 repos:
   - repo: https://github.com/psf/black
-    rev: 21.7b0
+    rev: 21.8b0
     hooks:
       - id: black
         args: ["--target-version=py36"]
 
   - repo: https://github.com/asottile/blacken-docs
-    rev: v1.10.0
+    rev: v1.11.0
     hooks:
       - id: blacken-docs
         args: ["--target-version=py36"]