Fix failing black test (#10697)

* Fix failing black test

.pre-commit-config.yaml

@@ -150,7 +150,7 @@ repos:
     hooks:
       - id: check-hooks-apply
   - repo: https://github.com/psf/black
-    rev: stable
+    rev: 19.10b0
     hooks:
       - id: black
         files: api_connexion/.*\.py|.*providers.*\.py