The travis build for s390x started to fail with:

Failed to fetch http://security.debian.org/debian-security/dists/jessie/updates/InRelease Unable to find expected entry 'main/binary-s390x/Packages' in Release file (Wrong sources.list entry or malformed file)

This changes the repository definition just like it is done for ppc64le.
Signed-off-by: Adrian Reber <areber@redhat.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>