MDL-57321 theme_boost: Fix improperly nested ul elements in footer

theme/boost/templates/custom_menu_footer.mustache

@@ -8,8 +8,10 @@
             {{/url}}
         {{/divider}}
         {{#haschildren}}
-            <ul class="list-unstyled m-l-1">
-                {{> theme_boost/custom_menu_footer }}
-            </ul>
+            <li>
+                <ul class="list-unstyled m-l-1">
+                    {{> theme_boost/custom_menu_footer }}
+                </ul>
+            </li>
         {{/haschildren}}
     {{/children}}