[NOP] added missing @Override annotation 

I forgot this one to add to the getID method when adding this method to
the ISarosSession interface.

Change-Id: Iba5563a0c817b6d57286d272bf9648db575f14cf
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1137
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>
Tested-by: Jenkins CI