Update PHPDoc for RepositoryInterface::getChildren()

Fixes #2183

Author: AkenRoberts

src/Tree/RepositoryInterface.php

@@ -36,11 +36,11 @@ public function getNodesHierarchy($node = null, $direct = false, array $options
     /**
      * Get list of children followed by given $node
      *
-     * @param object $node        - if null, all tree nodes will be taken
-     * @param bool   $direct      - true to take only direct children
-     * @param string $sortByField - field name to sort by
-     * @param string $direction   - sort direction : "ASC" or "DESC"
-     * @param bool   $includeNode - Include the root node in results?
+     * @param object               $node - if null, all tree nodes will be taken
+     * @param bool                 $direct - true to take only direct children
+     * @param null|string|string[] $sortByField - field name(s) to sort by
+     * @param string               $direction - sort direction : "ASC" or "DESC"
+     * @param bool                 $includeNode - Include the root node in results?
      *
      * @return array - list of given $node children, null on failure
      */