Update nav.html

A `navigation-list-child-list` is not displayed unless the enclosing `navigation-list-item` is `active`, so it needs to be generated only when `page.url == node.url or page.parent == node.title or page.grand_parent == node.title`.

_includes/nav.html

@@ -10,6 +10,7 @@
             {%- endif -%}
             <a href="{{ node.url | absolute_url }}" class="navigation-list-link{% if page.url == node.url %} active{% endif %}">{{ node.title }}</a>
             {%- if node.has_children -%}
+            {%- if page.url == node.url or page.parent == node.title or page.grand_parent == node.title -%}
               {%- assign children_list = site.html_pages | where: "parent", node.title | sort:"nav_order" -%}
               <ul class="navigation-list-child-list ">
                 {%- for child in children_list -%}
@@ -32,6 +33,7 @@
                 {%- endfor -%}
               </ul>
             {%- endif -%}
+            {%- endif -%}
           </li>
         {%- endif -%}
       {%- endunless -%}