Bump futures from 0.3.17 to 0.3.18

Bumps [futures](https://github.com/rust-lang/futures-rs) from 0.3.17 to 0.3.18.
- [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@0.3.17...0.3.18)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Cargo.lock

@@ -13,7 +13,7 @@ version = "0.3.0"
 
 [dependencies]
 clap = "2.33.3"
-futures = "0.3.17"
+futures = "0.3.18"
 tokio = { version = "1.8.1", features = ["full"] }
 hyper = { version = "0.14.15", features = ["stream"] }
 hyper_cgi = "0.2.1"