Update index.html

Author: leviding

2-ui/3-event-details/4-mouse-drag-and-drop/ball.view/index.html

@@ -13,7 +13,7 @@
 
 
   <script>
-    ball.onmousedown = function(event) { 
+    ball.onmousedown = function(event) {
       ball.style.position = 'absolute';
       ball.style.zIndex = 1000;
       document.body.appendChild(ball);