message: Fix CopyIn Future bound
diff: @@ -293,7 +293,8 @@ where
  impl<S> Future for CopyIn<S>
  where
  - S: Stream<Item = Vec<u8>>,
  + S: Stream,
  + S::Item: AsRef<[u8]>,
  S::Error: Into<Box<StdError + Sync + Send>>,
  {
  type Item = u64;
  