message: Fix `clock` example eventually skipping a second
diff: @@ -51,7 +51,7 @@ impl Application for Clock {
  }
  fn subscription(&self) -> Subscription<Message> {
  - time::every(std::time::Duration::from_millis(1000)).map(Message::Tick)
  + time::every(std::time::Duration::from_millis(500)).map(Message::Tick)
  }
  fn view(&mut self) -> Element<Message> {
  