message: nit refactoring
diff: @@ -108,7 +108,7 @@ struct OptFmt<T>(Option<T>);
  impl<T: fmt::Display> fmt::Display for OptFmt<T> {
  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  - if let Some(ref t) = self.0 {
  + if let Some(t) = &self.0 {
  fmt::Display::fmt(t, f)
  } else {
  f.write_str("-")
  