fix: param type

Author: yajra

src/DataTableAbstract.php

@@ -173,7 +173,7 @@ public static function create($source)
 
     /**
      * @param  string|array  $columns
-     * @param  string|\Yajra\DataTables\Contracts\Formatter  $formatter
+     * @param  string|callable|\Yajra\DataTables\Contracts\Formatter  $formatter
      * @return $this
      */
     public function formatColumn($columns, $formatter): static