enabled sidebar accordion in docs

docs/_includes/sidebar.html

@@ -5,7 +5,7 @@
     </a>
     <div class="sidebar">
       <nav class="mt-2">
-        <ul class="nav nav-pills nav-sidebar nav-child-indent flex-column" data-widget="treeview" role="menu" data-accordion="false">
+        <ul class="nav nav-pills nav-sidebar nav-child-indent flex-column" data-widget="treeview" role="menu" data-accordion="true">
          {% for item in site.navigation %}
             {% assign subitem_active = 'false' %}
             {% for subitem in item.subitems %}