chore(docsrs): make docs.rs build work

The nightly feature has been removed in rust 1.92, see docs.rs build
failure https://docs.rs/crate/rustls-native-certs/latest/builds/2773223
and rust PR rust-lang/rust#138907.

Author: joshuachp

src/lib.rs

@@ -19,7 +19,7 @@
 //! ```
 
 // Enable documentation for all features on docs.rs
-#![cfg_attr(docsrs, feature(doc_cfg, doc_auto_cfg))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
 use std::error::Error as StdError;
 use std::path::{Path, PathBuf};