message: Make `clock` example responsive
diff: @@ -66,16 +66,12 @@ impl Application for Clock {
  }
  fn view(&mut self) -> Element<Message> {
  - let canvas = Canvas::new(self)
  - .width(Length::Units(400))
  - .height(Length::Units(400));
  + let canvas = Canvas::new(self).width(Length::Fill).height(Length::Fill);
  Container::new(canvas)
  .width(Length::Fill)
  .height(Length::Fill)
  .padding(20)
  - .center_x()
  - .center_y()
  .into()
  }
  }
  