why the fixed body position is updated? #193

 const world = new CANNON.World({
 gravity: new CANNON.Vec3(0, -9.81, 0),
 });
 // box
 const boxBody = new CANNON.Body({
 mass: 1,
 shape: new CANNON.Box(new CANNON.Vec3(2, 2, 2)),
 });
 boxBody.position.set(2, 0, -2);
 world.addBody(boxBody);
 // ground
 const groundBody = new CANNON.Body({
 shape: new CANNON.Plane(new CANNON.Vec3(10, 10)),
 });
 groundBody.quaternion.setFromEuler(-Math.PI / 2, 0, 0); // 绕x轴旋转90度
 world.addBody(groundBody);
 const tick = () => {
 world.fixedStep();
 console.log(`boxBody.x: ${boxBody.position.x}`);
 cannonDebugger.update();
 window.requestAnimationFrame(tick);
 };
 tick();