fixes menu link missing navbar-nav

add navbar-nav class to ul tag when create menu link use bootstrap3

flask_admin/templates/bootstrap3/admin/base.html

@@ -51,7 +51,7 @@
           {% endblock %}
 
           {% block menu_links %}
-          <ul class="nav navbar-right">
+          <ul class="nav navbar-nav navbar-right">
             {{ layout.menu_links() }}
           </ul>
           {% endblock %}