Bump flask-migrate from 2.2.0 to 2.2.1 in /{{cookiecutter.app_name}}

Bumps [flask-migrate](https://github.com/miguelgrinberg/flask-migrate) from 2.2.0 to 2.2.1.
- [Release notes](https://github.com/miguelgrinberg/flask-migrate/releases)
- [Changelog](https://github.com/miguelgrinberg/Flask-Migrate/blob/master/CHANGELOG.md)
- [Commits](https://github.com/miguelgrinberg/flask-migrate/compare/v2.2.0...v2.2.1

)

Signed-off-by: dependabot[bot] <support@dependabot.com>