Updating the dinosaur's displacement and velocity in update()

dino.dart

@override
void update(Duration lastTime, Duration elapsedTime) {
  double elapsedSeconds =
      ((elapsedTime.inMilliseconds - lastTime.inMilliseconds) / 1000);
 
  dispY += velY * elapsedSeconds;
  if (dispY <= 0) {
    dispY = 0;
    velY = 0;
  } else {
    velY -= GRAVITY_PPSPS * elapsedSeconds;
  }
 
  frame = (elapsedTime.inMilliseconds / 100).floor() % 2 + 3 
}