Bump rusb from 0.9.3 to 0.9.4 in /rust (#56)

Bumps [rusb](https://github.com/a1ien/rusb) from 0.9.3 to 0.9.4.
- [Changelog](https://github.com/a1ien/rusb/blob/master/CHANGELOG.md)
- [Commits](https://github.com/a1ien/rusb/commits)

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

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