Bump diesel from 1.4.3 to 1.4.8

Bumps [diesel](https://github.com/diesel-rs/diesel) from 1.4.3 to 1.4.8.
- [Release notes](https://github.com/diesel-rs/diesel/releases)
- [Changelog](https://github.com/diesel-rs/diesel/blob/master/CHANGELOG.md)
- [Commits](diesel-rs/diesel@v1.4.3...v1.4.8)

---
updated-dependencies:
- dependency-name: diesel
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>