Bump flask from 1.1.0 to 1.1.1 in /{{cookiecutter.app_name}}

Bumps [flask](https://github.com/pallets/flask) from 1.1.0 to 1.1.1.
- [Release notes](https://github.com/pallets/flask/releases)
- [Changelog](https://github.com/pallets/flask/blob/master/CHANGES.rst)
- [Commits](https://github.com/pallets/flask/compare/1.1.0...1.1.1

)

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