Bump supertest from 6.2.4 to 6.3.0

Bumps [supertest](https://github.com/visionmedia/supertest) from 6.2.4 to 6.3.0.
- [Release notes](https://github.com/visionmedia/supertest/releases)
- [Commits](https://github.com/visionmedia/supertest/compare/v6.2.4...v6.3.0)