buildroot

imagemagick: security bump to version 6.7.8-8

Fixes CVE-2012-3437, CVE-2012-3437 and CVE-2012-3438.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>