build(deps): bump tokio from 0.1.20 to 0.1.22

Bumps [tokio](https://github.com/tokio-rs/tokio) from 0.1.20 to 0.1.22.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](https://github.com/tokio-rs/tokio/commits)

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

Author: dependabot-preview[bot]

Cargo.lock

@@ -40,7 +40,7 @@ slog-async = "2.3.0"
 slog-envlogger = "2.1.0"
 slog-term = "2.4.1"
 tiny-keccak = "1.4.2"
-tokio = "0.1.20"
+tokio = "0.1.22"
 tokio-executor = "0.1.5"
 tokio-retry = "0.2"
 tokio-timer = "0.2.11"