Bump sequelize from 4.32.2 to 5.15.1

Bumps [sequelize](https://github.com/sequelize/sequelize) from 4.32.2 to 5.15.1.
- [Release notes](https://github.com/sequelize/sequelize/releases)
- [Commits](sequelize/sequelize@v4.32.2...v5.15.1)

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

Author: dependabot[bot]