Use doc_auto_cfg instead of doc_cfg (#392)

Author: newpavlov

src/custom.rs

@@ -65,7 +65,6 @@ use core::{mem::MaybeUninit, num::NonZeroU32};
 /// [top-level documentation](index.html#custom-implementations) this
 /// registration only has an effect on unsupported targets.
 #[macro_export]
-#[cfg_attr(docsrs, doc(cfg(feature = "custom")))]
 macro_rules! register_custom_getrandom {
     ($path:path) => {
         // TODO(MSRV 1.37): change to unnamed block

src/error_impls.rs

@@ -1,4 +1,3 @@
-#![cfg_attr(docsrs, doc(cfg(feature = "std")))]
 extern crate std;
 
 use crate::Error;

src/lib.rs

@@ -190,7 +190,7 @@
 )]
 #![no_std]
 #![warn(rust_2018_idioms, unused_lifetimes, missing_docs)]
-#![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
 
 #[macro_use]
 extern crate cfg_if;