chore: fix feature gating

Author: aatifsyed

src/peeking_take_while.rs

@@ -266,7 +266,7 @@ peeking_next_by_clone! { ['a, K, V] std::collections::hash_map::Iter<'a, K, V> }
 peeking_next_by_clone! { ['a, K, V] std::collections::hash_map::Keys<'a, K, V> }
 #[cfg(feature = "use_std")]
 peeking_next_by_clone! { ['a, K, V] std::collections::hash_map::Values<'a, K, V> }
-
+#[cfg(feature = "use_std")]
 peeking_next_by_clone! { ['a, T] std::collections::hash_set::Iter<'a, T> }
 
 // cloning a Rev has no extra overhead; peekable and put backs are never DEI.