[pre-commit.ci] pre-commit autoupdate (jpadilla#572)

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

@@ -6,7 +6,7 @@ repos:
         args: ["--target-version=py36"]
 
   - repo: https://github.com/asottile/blacken-docs
-    rev: v1.9.0
+    rev: v1.9.1
     hooks:
       - id: blacken-docs
         args: ["--target-version=py36"]