Replace doc_auto_cfg nightly feature with doc_cfg

Signed-off-by: Denis Varlakov <[email protected]>

Author: survived

src/lib.rs

@@ -7,7 +7,7 @@
     trivial_casts,
     trivial_numeric_casts
 )]
-#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 #![no_std]
 
 //! A crate for generating large prime numbers, suitable for cryptography.