Update tokio requirement from 0.1.7 to 0.2.4

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-0.1.7...tokio-0.2.4)

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

Author: dependabot-preview[bot]

amadeus-aws/Cargo.toml

@@ -34,7 +34,7 @@ rusoto_core = "0.42"
 rusoto_s3 = "0.42"
 serde_closure = "0.2"
 serde = { version = "1.0", features = ["derive"] }
-tokio = "0.1.7"
+tokio = "0.2.4"
 tokio-retry = "0.2"
 url = { version = "2.1", features = ["serde"] }