优化公用函数

src/controls/thumbnails.js

@@ -52,8 +52,8 @@ export default class Thumbnails {
   }
 
   showThumbnails(event) {
-    const { $progress } = this.art.refs;
-    const { width: posWidth } = this.getPosFromEvent(event);
+    const { refs: { $progress }, controls } = this.art;
+    const { width: posWidth } = controls.progress.getPosFromEvent(event);
     const { url, height, width, number, column } = this.art.option.thumbnails;
     const perWidth = $progress.clientWidth / number;
     const perIndex = Math.ceil(posWidth / perWidth);