WikimediaUI theme: Fix miscalculated frameless button's icon position
WikimediaUI theme: Fix miscalculated frameless button's icon position

Fixing frameless ButtonWidget's icon and `:first-child` position,
which I've miscalculated in If5722df41e75.

Change-Id: I863e76e658854399947fa17a47248362e387a7d4

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui