clear board before drawing

src/lib.rs

@@ -50,6 +50,7 @@ pub fn start() {
             Some(date) if (Date::now() - date) < 250. => (),
             _ => {
                 timestamp = Some(Date::now());
+                context.clear_rect(0., 0., canvas.width() as f64, canvas.height() as f64);
                 context.begin_path();  
                 let iter = CircleShapes::new(modulo, factor, Circle {center: Point {x: 400.0, y: 400.0}, radius: 400.0});
                 for shape in iter {