fix(deps): update rust crate tokio to 1.15.0 (#3859)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

src/functions-templates/rust/hello-world/Cargo.toml

@@ -11,4 +11,4 @@ http = "0.2.5"
 lambda_runtime = "0.4.1"
 log = "0.4.14"
 simple_logger = "1.16.0"
-tokio = "1.14.0"
+tokio = "1.15.0"