Fix Warning in PHP < 5.4

For PHP versions < 5.4, filter_input_array has two parameters, not three (see http://php.net/manual/en/function.filter-input-array.php).
Change adds a check for the PHP version and will not include the third argument if the version does not support it.
The error occurs when you attempt to add a post type archive to a menu. Instead, it spawns an error:
Warning: filter_input_array() expects at most 2 parameters, 3 given in /[...]/plugins/post-type-archive-links/post-type-archive-links.php on line 363.