Bump psycopg2 from 2.7.7 to 2.8 in /{{cookiecutter.app_name}}

Bumps [psycopg2](https://github.com/psycopg/psycopg2) from 2.7.7 to 2.8.
- [Release notes](https://github.com/psycopg/psycopg2/releases)
- [Changelog](https://github.com/psycopg/psycopg2/blob/master/NEWS)
- [Commits](https://github.com/psycopg/psycopg2/commits

)

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