Bump pep8-naming in /{{cookiecutter.app_name}}/requirements

Bumps [pep8-naming](https://github.com/PyCQA/pep8-naming) from 0.8.2 to 0.9.0.
- [Release notes](https://github.com/PyCQA/pep8-naming/releases)
- [Changelog](https://github.com/PyCQA/pep8-naming/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/PyCQA/pep8-naming/compare/0.8.2...0.9.0

)

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