package/snowball-init: use github helper

Otherwise download is broken:

>>> snowball-init b064be21de25729039e5e54037bbdd2e25cfd5b7 Downloading
--2016-01-31 17:31:27--  https://github.com/igloocommunity/snowball-init/snowball-init-b064be21de25729039e5e54037bbdd2e25cfd5b7.tar.gz


Resolving github.com (github.com)... 192.30.252.128
Connecting to github.com (github.com)|192.30.252.128|:443... connected.
HTTP request sent, awaiting response... 404 Not Found
2016-01-31 17:31:27 ERROR 404: Not Found.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>