Bump alembic from 1.3.0 to 1.3.1

Bumps [alembic](https://github.com/sqlalchemy/alembic) from 1.3.0 to 1.3.1.
- [Release notes](https://github.com/sqlalchemy/alembic/releases)
- [Changelog](https://github.com/sqlalchemy/alembic/blob/master/CHANGES)
- [Commits](https://github.com/sqlalchemy/alembic/commits)

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

requirements.txt

@@ -13,5 +13,5 @@ icalevents==0.1.23
 icalendar==4.0.4
 sqlalchemy==1.3.10
 filelock==3.0.12
-alembic==1.3.0
+alembic==1.3.1
 numpy==1.17.4