Unifying black version in pre-commit config file (#6413)

Unifying black version in pre-commit config file

Author: nicoddemus

.pre-commit-config.yaml

@@ -8,7 +8,7 @@ repos:
     rev: v1.0.0
     hooks:
     -   id: blacken-docs
-        additional_dependencies: [black==19.3b0]
+        additional_dependencies: [black==19.10b0]
 -   repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v2.2.3
     hooks: