fix: delete use of removed doc_auto_cfg feature (#309)

Author: abonander

src/lib.rs

@@ -1,6 +1,5 @@
 #![doc = include_str!("../README.md")]
 #![cfg_attr(docsrs, feature(doc_cfg))]
-#![cfg_attr(docsrs, feature(doc_auto_cfg))]
 
 #[macro_use]
 extern crate static_assertions;