zbar: fix build with Fedora 29
    
    There is a bug at pygobject-codegen-2.0 related to its dependency
    on having a working /usr/bin/python with prevents zbar to be built.
    
    Add a hack to make it work.
    
    While here, update it to reflect the latest changes at zbar
    upstream.
    
    Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>