Minor tweak

Author: javiereguiluz

service_container/service_subscribers_locators.rst

@@ -293,6 +293,7 @@ argument of type ``service_locator``:
 
             $services->set(CommandBus::class)
                 ->args([service_locator([
+                    // In versions earlier to Symfony 5.1 the service() function was called ref()
                     'App\FooCommand' => service('app.command_handler.foo'),
                     'App\BarCommand' => service('app.command_handler.bar'),
                     // if the element has no key, the ID of the original service is used