build(deps): update tokio requirement from ~0.3 to ~1.4

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](tokio-rs/tokio@tokio-0.3.0...tokio-1.4.0)

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

examples/Cargo.toml

@@ -14,7 +14,7 @@ futures-timer = "^3.0"
 
 futures = "^0.3"
 smol = "^1.2"
-tokio = { version = "^0.3", features = ["full"] }
+tokio = { version = "^1.4", features = ["full"] }
 async-std = { version = "^1.7", features = ["attributes"] }
 
 ptree = { version = "0.3", default-features = false, features = ["ansi"] }