Zend\Filter\Compress\Tar::setMode() would not work

[sasezaki]

<?php
$tar = new Zend\Filter\Compress\Tar;
$tar->setTarget(__DIR__.'/data.txt');
$tar->setArchive(__DIR__.'/data.tar.gz');
$tar->setMode('gz');
$tar->compress('compress me');

will raise error

PHP Fatal error:  Uncaught exception 'Zend\Filter\Exception\RuntimeException' with message 'Error creating the Tar archive' in /home/sasezaki/dev/zendframework_zf2/library/Zend/Filter/Compress/Tar.php:188

Because setMode() keeps mode as ucfirst(strtolower($mode)).
and Archive_Tar accepts only strtolowers.

This issue will be raise zf1, too.