minor stylefix for base_list template, to correctly display the "All elements" checkbox

Resources/views/CRUD/base_list.html.twig

@@ -151,7 +151,7 @@ file that was distributed with this source code.
                                 {% endfor %}
                             </select>
 
-                            <label>
+                            <label class="checkbox">
                                 <input type="checkbox" name="all_elements"/>
                                 {% trans from 'SonataAdminBundle' %}all_elements{% endtrans %}
                             </label>