Update tokio-util requirement from 0.6 to 0.7

Updates the requirements on [tokio-util](https://github.com/tokio-rs/tokio) to permit the latest version.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](https://github.com/tokio-rs/tokio/commits)

---
updated-dependencies:
- dependency-name: tokio-util
  dependency-type: direct:production
...

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

Cargo.toml

@@ -22,7 +22,7 @@ bytes = { version = "1", optional = true }
 futures-io = { version = "0.3.4", optional = true }
 futures-util = { version = "0.3.4", features = ["io"], optional = true }
 asynchronous-codec = { version = "0.6", optional = true }
-tokio-util = { version = "0.6", features = ["codec"], optional = true }
+tokio-util = { version = "0.7", features = ["codec"], optional = true }
 nom = { version = "7", optional = true }
 
 [dev-dependencies]