Add new Polish translation for DEFAULTSORT magic word

This has been done on translatewiki ages ago [1], I was under the
impression that this is updated with the regular localisation updates, but
apparently not so. The Polish Wikipedia community would like to have
started using the new translation a week ago [2], so let's expedite this
please.

[1] https://translatewiki.net/w/i.php?title=MediaWiki%3ASp-translate-data-MagicWords%2Fpl&diff=5944044&oldid=5711187
[2] https://pl.wikipedia.org/wiki/Wikipedia:Kawiarenka/Kwestie_techniczne#DEFAULTSORT_-_mo.C5.BCe_przet.C5.82umaczy.C4.87.3F

Change-Id: I52f9f5962d3b52d7a5e9b16915f7dedabeecd142