Improve test coverage

packages/scrollbar/src/bar.js

@@ -1,6 +1,7 @@
 import { on, off } from 'element-ui/src/utils/dom';
 import { renderThumbStyle, BAR_MAP } from './util';
 
+/* istanbul ignore next */
 export default {
   name: 'Bar',
 

packages/scrollbar/src/main.js

@@ -5,6 +5,7 @@ import scrollbarWidth from 'element-ui/src/utils/scrollbar-width';
 import * as util from './util';
 import Bar from './bar';
 
+/* istanbul ignore next */
 export default {
   name: 'ElScrollbar',