Remove doc_auto_cfg

doc_auto_cfg was merged into doc_cfg in rust-lang/rust#138907

Author: bilelmoussaoui

src/lib.rs

@@ -91,7 +91,7 @@
 #![deny(missing_docs)]
 #![deny(meta_variable_misuse)]
 #![no_std]
-#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
 pub extern crate typenum;