Update src/stream/double_ended_stream.rs

Co-Authored-By: Stjepan Glavina <stjepang@gmail.com>

Author: yoshuawuyts

src/stream/double_ended_stream.rs

@@ -11,7 +11,7 @@ use std::task::{Context, Poll};
 ///
 /// [`Stream`]: trait.Stream.html
 #[cfg_attr(feature = "docs", doc(cfg(unstable)))]
-#[cfg(feature = "unstable")]
+#[cfg(any(feature = "unstable", feature = "docs"))]
 pub trait DoubleEndedStream: Stream {
     /// Removes and returns an element from the end of the stream.
     ///