switch to ES6 modules and fix canvas name

spline.ts

@@ -33,7 +33,7 @@ function draw(ctx: CanvasRenderingContext2D, points: Point[]) {
 }
 
 function init() {
-    const canvas = document.getElementById("game") as HTMLCanvasElement | null;
+    const canvas = document.getElementById("canvas") as HTMLCanvasElement | null;
     if (!canvas) throw new Error("unable to get canvas HTML element");
 
     const ctx = canvas.getContext("2d") as CanvasRenderingContext2D | null;