message: Fix nightly warning about unnecessary parenthesis
diff: @@ -435,7 +435,7 @@ where
  {
  type Item = NnzEither<'a, N1, N2>;
  - fn next(&mut self) -> Option<(NnzEither<'a, N1, N2>)> {
  + fn next(&mut self) -> Option<NnzEither<'a, N1, N2>> {
  match (self.left.peek(), self.right.peek()) {
  (None, Some(&(_, _))) => {
  let (rind, rval) = self.right.next().unwrap();
  