Polish branding - fix langpack mac installer icon

Fix for fdo#33229 - the lang pack installer icon on mac was still
showing seagulls.
Signed-off-by: Fridrich Štrba <fridrich.strba@bluewin.ch>
(cherry picked from commit 44c6333a2b6923add66d70be6329a6ad4f3aa66d)
Signed-off-by: Michael Meeks <michael.meeks@novell.com>
Signed-off-by: Christian Lohmaier <lohmaier@googlemail.com>