fix the video link in doc

docs/guide/rig.md

@@ -37,4 +37,4 @@ To associate a target position with a joint, select `Add IK` and edit the target
 In the [animate](/docs/guide/animate.md) mode, once inverse kinematics is implemented, joint rotation(pose) is updated based on the enabled IK handles.
 
 <video src="rigging_mode/guide-ik.mp4" controls preload muted loop style="max-width: 100%; margin: 0 auto;"></video>
-![](./rigging_mode/guide-ik.mov)
+![](./rigging_mode/guide-ik.mp4)