python-meld3: fix setup type

meld3 relies on setuptools instead of distutils.

Fixes:
http://autobuild.buildroot.net/results/f9e/f9ef01d2cb1d32cb13743e83c7fc9c0d354fc571/



Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>