message: Fix `error:`/`warning:` coloring inconsistency with rustc
diff: @@ -210,14 +210,14 @@ impl Shell {
  if self.needs_clear {
  self.err_erase_line();
  }
  - self.err.print(&"error:", Some(&message), Red, false)
  + self.err.print(&"error", Some(&message), Red, false)
  }
  /// Prints an amber 'warning' message.
  pub fn warn<T: fmt::Display>(&mut self, message: T) -> CargoResult<()> {
  match self.verbosity {
  Verbosity::Quiet => Ok(()),
  - _ => self.print(&"warning:", Some(&message), Yellow, false),
  + _ => self.print(&"warning", Some(&message), Yellow, false),
  }
  }
  @@ -318,6 +318,8 @@ impl ShellOut {
  write!(stream, "{:>12}", status)?;
  } else {
  write!(stream, "{}", status)?;
  + stream.set_color(ColorSpec::new().set_bold(true))?;
  + write!(stream, ":")?;
  }
  stream.reset()?;
  match message {
  @@ -329,7 +331,7 @@ impl ShellOut {
  if justified {
  write!(w, "{:>12}", status)?;
  } else {
  - write!(w, "{}", status)?;
  + write!(w, "{}:", status)?;
  }
  match message {
  Some(message) => writeln!(w, " {}", message)?,
  