Bump prometheus from 0.13.4 to 0.14.0

Bumps [prometheus](https://github.com/tikv/rust-prometheus) from 0.13.4 to 0.14.0.
- [Changelog](https://github.com/tikv/rust-prometheus/blob/master/CHANGELOG.md)
- [Commits](tikv/rust-prometheus@v0.13.4...v0.14.0)

---
updated-dependencies:
- dependency-name: prometheus
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]