fix: rename doc_auto_cfg feature (#737)

Author: JohnTitor

actix-tls/src/lib.rs

@@ -2,7 +2,7 @@
 
 #![doc(html_logo_url = "https://actix.rs/img/logo.png")]
 #![doc(html_favicon_url = "https://actix.rs/favicon.ico")]
-#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
 #[cfg(feature = "openssl")]
 #[allow(unused_extern_crates)]