Added callable to ReferencedNameHelper

Author: kukulich

SlevomatCodingStandard/Helpers/ReferencedNameHelper.php

@@ -80,6 +80,7 @@ private static function createAllReferencedNames(PHP_CodeSniffer_File $phpcsFile
 						'integer',
 						'bool',
 						'boolean',
+						'callable',
 					], true);
 				});
 				foreach ($referencedNames as $name) {