Update blacken-docs repo in pre-commit conf after owner transfer. (#451)

Author: stefmolin

.pre-commit-config.yaml

@@ -28,7 +28,7 @@ repos:
         files: \.(html|md|yml|yaml)
         args: [--prose-wrap=preserve]
 
-  - repo: https://github.com/asottile/blacken-docs
+  - repo: https://github.com/adamchainz/blacken-docs
     rev: 1.13.0
     hooks:
       - id: blacken-docs