Add support for ordering using compound key

Author: yajra

src/yajra/Datatables/Engines/CollectionEngine.php

@@ -99,7 +99,7 @@ public function ordering()
                 function ($row) use ($column) {
                     $row = Helper::castToArray($row);
 
-                    return $row[$column];
+                    return Arr::get($row, $column);
                 }
             );