message: sound.play() requires mut
diff: @@ -54,7 +54,7 @@ impl MainState {
  let font = graphics::Font::new(ctx, "/DejaVuSerif.ttf").unwrap();
  let text = graphics::Text::new(("Hello world!", font, 48.0));
  - let sound = audio::Source::new(ctx, "/sound.ogg").unwrap();
  + let mut sound = audio::Source::new(ctx, "/sound.ogg").unwrap();
  let pixel_sized_text =
  graphics::Text::new(("This text is 32 pixels high", font, 32.0));
  