Bump prost from 0.13.3 to 0.13.4

Bumps [prost](https://github.com/tokio-rs/prost) from 0.13.3 to 0.13.4.
- [Release notes](https://github.com/tokio-rs/prost/releases)
- [Changelog](https://github.com/tokio-rs/prost/blob/master/CHANGELOG.md)
- [Commits](tokio-rs/prost@v0.13.3...v0.13.4)

---
updated-dependencies:
- dependency-name: prost
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]