Corrects a cfg feature declaration in task/mod.rs

src/task/mod.rs

@@ -25,7 +25,7 @@
 #[doc(inline)]
 pub use std::task::{Context, Poll, Waker};
 
-#[cfg(feature = "unstable")]
+#[cfg(any(feature = "unstable", feature = "docs"))]
 #[cfg_attr(feature = "docs", doc(cfg(unstable)))]
 #[doc(inline)]
 pub use async_macros::ready;