Updated mediawiki/extensions
Project: mediawiki/extensions/BetaFeatures  f54938bf71fd1382ad8904251002a0d219f541eb

White background for the green Beta checkboxes

Background color set to white to make the checkboxes look a bit
more like actual checkboxes. Otherwise the background is gray and
the light green checkbox are hard to see depending on the current
skin and possible user CSS.

Change-Id: I9720a9846527788d1219e450d08b0703bab635fc