Bump express from 4.16.2 to 4.20.0 in /fixtures/packaging/brunch/prod

Bumps [express](https://github.com/expressjs/express) from 4.16.2 to 4.20.0.
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/master/History.md)
- [Commits](expressjs/express@4.16.2...4.20.0)

---
updated-dependencies:
- dependency-name: express
  dependency-type: indirect
...

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