Update duration

demos/hello-aframe/index.html

                     <!-- Magic circle -->
                     <a-plane width="4" height="4"
                         material="src: #magic-circle; color: #beefff; side: double; shader: flat; transparent: true; opacity: 1"
-                        animation="property: object3D.rotation.z; from: 360; to: 0; dur: 4000; loop: true; easing: linear">
+                        animation="property: object3D.rotation.z; from: 360; to: 0; dur: 8000; loop: true; easing: linear">
                     </a-plane>
 
                 </a-entity>

demos/hello-aframe/video.html

                     <!-- Magic circle -->
                     <a-plane width="4" height="4"
                         material="src: #magic-circle; color: #beefff; side: double; shader: flat; transparent: true; opacity: 1"
-                        animation="property: object3D.rotation.z; from: 360; to: 0; dur: 4000; loop: true; easing: linear">
+                        animation="property: object3D.rotation.z; from: 360; to: 0; dur: 8000; loop: true; easing: linear">
                     </a-plane>
 
                 </a-entity>