Update src/lib.rs

Co-Authored-By: Taiki Endo <te316e89@gmail.com>

Author: k-nasa

src/lib.rs

@@ -47,7 +47,6 @@
 #![doc(test(attr(allow(unused_extern_crates, unused_variables))))]
 #![doc(html_logo_url = "https://async.rs/images/logo--hero.svg")]
 #![recursion_limit = "2048"]
-#![feature(associated_type_bounds)]
 
 #[macro_use]
 mod utils;