buildroot

gd: security bump to version 2.2.4

Fixes:
CVE-2016-9317 - gdImageCreate() doesn't check for oversized images and
as such is prone to DoS vulnerabilities.
CVE-2016-6912 - double-free in gdImageWebPtr()
(without CVE):
Potential unsigned underflow in gd_interpolation.c
DOS vulnerability in gdImageCreateFromGd2Ctx()
Signed Integer Overflow gd_io.c

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>