interface: Use doc_cfg instead of doc_auto_cfg (#224)

Use doc_cfg instead of doc_auto_cfg

Author: febo

interface/src/lib.rs

@@ -1,7 +1,7 @@
 //! The Stake program interface.
 
 #![cfg_attr(feature = "frozen-abi", feature(min_specialization))]
-#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
 #[allow(deprecated)]
 pub mod config;