Update .pre-commit-config.yaml

Make Flake8 accept Black's reformatting, 
avoiding a doom loop when Black occasionally lengthens a line
you just shortened, above Flake8 (PEP 8?) limit.

https://black.readthedocs.io/en/stable/guides/using_black_with_other_tools.html#flake8

.pre-commit-config.yaml

@@ -43,6 +43,7 @@ repos:
     rev: 6.0.0
     hooks:
       - id: flake8
+        args: ['--max-line-length=88']
 
 ci:
   autoupdate_schedule: weekly