DX: rector in docs directory

docs/source/development/user-interface/widgets/ChillMainConfiguration.php

@@ -23,19 +23,12 @@ class ChillMainConfiguration implements ConfigurationInterface
 {
     use AddWidgetConfigurationTrait;
 
-    /**
-     * @var ContainerBuilder
-     */
-    private $containerBuilder;
-
     public function __construct(
         array $widgetFactories,
-        ContainerBuilder $containerBuilder
+        private ContainerBuilder $containerBuilder
     ) {
         // we register here widget factories (see below)
         $this->setWidgetFactories($widgetFactories);
-        // we will need the container builder later...
-        $this->containerBuilder = $containerBuilder;
     }
 
     public function getConfigTreeBuilder()