Bump futures-io from 0.3.18 to 0.3.21
Bumps [futures-io](https://github.com/rust-lang/futures-rs) from 0.3.18 to 0.3.21.
- [Release notes](https://github.com/rust-lang/futures-rs/releases)
- [Changelog](https://github.com/rust-lang/futures-rs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rust-lang/futures-rs/compare/0.3.18...0.3.21)
---
updated-dependencies:
- dependency-name: futures-io
dependency-type: indirect
update-type: version-update:semver-patch
...
Signed-off-by: dependabot[bot] <support@github.com>
dependabot[bot]