fix updates being slow when not moving the mouse

src/gui/ElevatorCanvas.java

@@ -47,6 +47,7 @@ class ElevatorCanvas extends JPanel {
 			g.setColor(Color.BLACK);
 		}
 		g.fillRect(0, y, WIDTH, HEIGHT);
+		Toolkit.getDefaultToolkit().sync();
     }
 
     public void setElevatorY(int y) {