fix(storybook): fix Hierarchical menu separator in Breadcrumb story (#3695)

If a separator is chosen which isn't the same as the corresponding hierarchical menu on the page, it will cause a conflict between those, and it will no longer be split correctly.

Author: tkrugg

stories/breadcrumb.stories.js

@@ -135,7 +135,6 @@ storiesOf('Breadcrumb', module)
       search.addWidget(
         instantsearch.widgets.breadcrumb({
           container: breadcrumb,
-          separator: ' / ',
           attributes: [
             'hierarchicalCategories.lvl0',
             'hierarchicalCategories.lvl1',