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

Bumps [werkzeug](https://github.com/pallets/werkzeug) from 0.15.6 to 0.16.0.
- [Release notes](https://github.com/pallets/werkzeug/releases)
- [Changelog](https://github.com/pallets/werkzeug/blob/master/CHANGES.rst)
- [Commits](https://github.com/pallets/werkzeug/compare/0.15.6...0.16.0

)

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