message: remove timer::sleep_until_next_frame from docs
diff: @@ -61,7 +61,7 @@ pub trait EventHandler {
  /// Called to do the drawing of your game.
  /// You probably want to start this with
  /// `graphics::clear()` and end it with
  - /// `graphics::present()` and `timer::sleep_until_next_frame()`
  + /// `graphics::present()` and `timer::yield_now()`
  fn draw(&mut self, _ctx: &mut Context) -> GameResult<()>;
  /// A mouse button was pressed
  