Address soundness issue in futures-util

This is technically a breaking change, but allowed since it fixes a
soundness issue in futures-util (rust-lang/futures-rs#2830).

Fixes #8.
Closes #9.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "streamunordered"
-version = "0.5.3"
+version = "0.5.4"
 authors = ["Jon Gjengset <jon@thesquareplanet.com>"]
 license = "MIT/Apache-2.0"
 edition = "2018"
@@ -20,7 +20,7 @@ maintenance = { status = "passively-maintained" }
 [dependencies]
 futures-core = "0.3.0"
 futures-sink = "0.3.0"
-futures-util = "0.3.0"
+futures-util = "0.3.31"
 slab = "0.4.0"
 
 [dev-dependencies]

src/lib.rs

@@ -738,7 +738,7 @@ where
     }
 }
 
-impl<S: Stream> Stream for StreamUnordered<S> {
+impl<S: Stream + 'static> Stream for StreamUnordered<S> {
     type Item = (StreamYield<S>, usize);
 
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
@@ -979,7 +979,7 @@ impl<S: Stream> FromIterator<S> for StreamUnordered<S> {
     }
 }
 
-impl<S: Stream> FusedStream for StreamUnordered<S> {
+impl<S: Stream + 'static> FusedStream for StreamUnordered<S> {
     fn is_terminated(&self) -> bool {
         self.is_terminated.load(Relaxed)
     }

src/task.rs

@@ -74,12 +74,14 @@ impl<S> ArcWake for Task<S> {
     }
 }
 
-impl<S> Task<S> {
+impl<S: 'static> Task<S> {
     /// Returns a waker reference for this task without cloning the Arc.
     pub(super) fn waker_ref(this: &Arc<Task<S>>) -> WakerRef<'_> {
         waker_ref(this)
     }
+}
 
+impl<S> Task<S> {
     /// Spins until `next_all` is no longer set to `pending_next_all`.
     ///
     /// The temporary `pending_next_all` value is typically overwritten fairly