message: chore(client): fix unused_mut warning in 1.18
diff: @@ -387,7 +387,7 @@ impl<T: Clone + Closed> Checkout<T> {
  let mut drop_parked = false;
  if let Some(ref mut rx) = self.parked {
  match rx.poll() {
  - Ok(Async::Ready(mut entry)) => {
  + Ok(Async::Ready(entry)) => {
  if !entry.value.is_closed() {
  return Ok(Async::Ready(self.pool.reuse(&self.key, entry)));
  }
  