Bump environs in /{{cookiecutter.app_name}}/requirements

Bumps [environs](https://github.com/sloria/environs) from 7.1.0 to 7.2.0.
- [Release notes](https://github.com/sloria/environs/releases)
- [Changelog](https://github.com/sloria/environs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sloria/environs/compare/7.1.0...7.2.0

)

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