Bump tokio from 0.2.22 to 0.3.1

Bumps [tokio](https://github.com/tokio-rs/tokio) from 0.2.22 to 0.3.1.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](tokio-rs/tokio@tokio-0.2.22...tokio-0.3.1)

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

Author: dependabot-preview[bot]

Cargo.lock

@@ -12,7 +12,7 @@ futures-util = { version = "0.3", default-features = false }
 hyper = { version = "0.13" }
 log = "0.4"
 sha-1 = "0.9"
-tokio = { version = "0.2", features = ["full", "sync", "time"] }
+tokio = { version = "0.3", features = ["full", "sync", "time"] }
 tokio-tungstenite = "0.11.0"
 toml = "0.5"
 serde = { version = "1.0", features = ["derive"] }