lowercase second character in digraph letters in IcuCollation tailorings

This is *the* valid way for Hungarian (per bug 45596 comment 10), and
it's likely more appropriate for other languages as well.

I should have done it this way in the first place; the original data
source includes these forms along with the all-uppercase ones (I
checked them all), so they're certainly at least not wrong. Just an
overlooking on my part.

Change-Id: Ie0ca297a082ddba8d757beb85655f86b3ee70b02