Apply fixes from StyleCI

Author: sdebacker

src/NestableCollection.php

@@ -17,9 +17,13 @@
 class NestableCollection extends Collection
 {
     private $total;
+
     private $parentColumn;
+
     private $removeItemsWithMissingAncestor = true;
+
     private $indentChars = '    ';
+
     private $childrenName = 'items';
 
     public function __construct($items = [])