Bump rustversion from 1.0.17 to 1.0.18

Bumps [rustversion](https://github.com/dtolnay/rustversion) from 1.0.17 to 1.0.18.
- [Release notes](https://github.com/dtolnay/rustversion/releases)
- [Commits](dtolnay/rustversion@1.0.17...1.0.18)

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

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