Bump futures from 0.3.12 to 0.3.13 (#23)

Bumps [futures](https://github.com/rust-lang/futures-rs) from 0.3.12 to 0.3.13. - [Release notes](https://github.com/rust-lang/futures-rs/releases) - [Changelog](https://github.com/rust-lang/futures-rs/blob/master/CHANGELOG.md) - [Commits](rust-lang/futures-rs@0.3.12...0.3.13) Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]