Fix formatting issues with black #1003

[viniciusdc]

Fixes #1018

Changes:

• black some missing files and format using flake8
• add an exception for traitlets config over testing actions

Put an x in the boxes that apply

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features to not work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

Would like a code change

[costrouc]

@viniciusdc could you add builtins to the setup.cfg instead so that it is used always with flake8. Instead of as a command line option.

[viniciusdc]

@viniciusdc could you add builtins to the setup.cfg instead so that it is used always with flake8. Instead of as a command line option.

Oh, thanks @costrouc, I totally forgot about it.