Bump futures from 0.3.7 to 0.3.8 (#507)

* Bump futures from 0.3.7 to 0.3.8

Bumps [futures](https://github.com/rust-lang/futures-rs) from 0.3.7 to 0.3.8.
- [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/0.3.7...0.3.8)

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

* Fix clippy.

* Fix more clippy.

* Fix clippy again?

* Cliipy yet again.

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>
Co-authored-by: Tomasz Drwięga <[email protected]>