Lighting items when uses more 2 level depth

Upgrade `isChildActive` method for lighting items when uses more 2 level depth.

Example: 
```php
            echo NavX::widget([
                'options' => ['class' => 'navbar-nav'],
                'encodeLabels' => false,
                'activateParents' => true,
                'items' => [
                    [
                        'label' => Icon::show('reorder') . Yii::t('app', 'Modules'),
                        'items' => [
                            [
                                'label' => Icon::show('image') . Yii::t('app', 'Photos'),
                                'items' => [
                                    [
                                        'label' => Icon::show('sort-alpha-asc') . Yii::t('app', 'All'),
                                        'url' => ['/photo-ideas/default/index'],
                                    ],
                                    [
                                        'label' => Icon::show('folder') . Yii::t('app', 'Categories'),
                                        'url' => ['/photo-ideas/categories/index'],
                                    ],
                                ],
                            ],
                        ],
                    ]
                ],
            ]);
```