Update VE core submodule to master (cfd855e)

New changes:
21bba98 update-oojs-ui.sh: Exclude the minimised distribution files
d9114f9 Update OOjs UI to v0.1.0-pre (48980881f3)
3ebaade Localisation updates from https://translatewiki.net.
2a2e256 Update OOjs UI to v0.1.0-pre (26dadbc60f)
517ebb0 Emit change event when dimensions change in MediaSizeWidget

Change-Id: Id30517765563547df92d2f432307fc7e719d05c8