Change homepage link (#389)

Author: k-nasa

Cargo.toml

@@ -9,7 +9,7 @@ authors = [
 edition = "2018"
 license = "Apache-2.0/MIT"
 repository = "https://github.com/async-rs/async-std"
-homepage = "https://github.com/async-rs/async-std"
+homepage = "https://async.rs"
 documentation = "https://docs.rs/async-std"
 description = "Async version of the Rust standard library"
 keywords = ["async", "await", "future", "std", "task"]