pre-commit: upgrade black

This brings psf/black#826, which helps with
psf/black#601.

Author: blueyed

.pre-commit-config.yaml

@@ -1,7 +1,7 @@
 exclude: doc/en/example/py2py3/test_py2.py
 repos:
 -   repo: https://github.com/psf/black
-    rev: 19.3b0
+    rev: 19.10b0
     hooks:
     -   id: black
         args: [--safe, --quiet]