Merge pull request #1577 from rust-lang/dependabot/cargo/futures-io-0.3.21

Bump futures-io from 0.3.18 to 0.3.21

Cargo.lock

@@ -533,9 +533,9 @@ dependencies = [
 
 [[package]]
 name = "futures-io"
-version = "0.3.18"
+version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e481354db6b5c353246ccf6a728b0c5511d752c08da7260546fc0933869daa11"
+checksum = "fc4045962a5a5e935ee2fdedaa4e08284547402885ab326734432bed5d12966b"
 
 [[package]]
 name = "futures-macro"