GF-56619: fix ISO code for Polish

The code had "po" for Polish, but the ISO 639 code for Polish is
actually "pl". This bug causes Polish to appear in the UI with
Miso/Museo Sans instead of LG Display because the
enyo-locale-non-latin CSS class is not placed on the body tag
properly.
Merge pull request #34 from enyojs/GF-56619

GF-56619: fix ISO code for Polish

Reviewed-By: Ben Combee (ben.combee@lge.com)