Fixed some deprecations.

src/DataTables/Column/MarkdownColumn.php

@@ -58,6 +58,7 @@ class MarkdownColumn extends AbstractColumn
      * The normalize function is responsible for converting parsed and processed data to a datatables-appropriate type.
      *
      * @param mixed $value The single value of the column
+     * @return mixed
      */
     public function normalize($value)
     {