Bump flask from 1.0.2 to 1.0.3 in /{{cookiecutter.app_name}}

Bumps [flask](https://github.com/pallets/flask) from 1.0.2 to 1.0.3.
- [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/1.0.2...1.0.3

)

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