Update tokio requirement from 0.2.22 to 0.3.5

Updates the requirements on [tokio](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)

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

Cargo.toml

@@ -36,7 +36,7 @@ serde = "1.0"
 serde_derive = "1.0"
 serde-big-array = "0.3.0"
 siphasher = "0.3"
-tokio = { version = "0.2.22", features = ["fs", "rt-threaded", "time", "tcp", "udp", "stream", "parking_lot"] }
+tokio = { version = "0.3.5", features = ["fs", "rt-threaded", "time", "tcp", "udp", "stream", "parking_lot"] }
 toml = "0.5"
 
 [dependencies.prometheus]