Feature doc_auto_cfg is merged into doc_cfg in the latest nightly

Upstream PR: rust-lang/rust#138907

Author: SpriteOvO

spdlog/src/lib.rs

@@ -277,7 +277,7 @@
 
 #![allow(unexpected_cfgs)]
 // Credits: https://blog.wnut.pw/2020/03/24/documentation-and-unstable-rustdoc-features/
-#![cfg_attr(all(doc, CHANNEL_NIGHTLY), feature(doc_auto_cfg))]
+#![cfg_attr(all(doc, CHANNEL_NIGHTLY), feature(doc_cfg))]
 #![warn(missing_docs)]
 
 // Used for referencing from proc-macros