libxkbcommon: Update to version 0.4.2.

Fixes build of i3lock and to possibly prevent breakage of other
packages, I've tested building of gtk3 and qt5 (partial, core2duo here).
I know it's not a comprehensive test but we can still revert in case
Hydra reports more builds failing.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>