libksba: security bump to version 1.3.4

Fixes:
CVE-2016-4356 - Fix encoding of invalid utf-8 strings in
dn.c" and "read access out of bounds".

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