Use the new debian-s390x-cross.docker target to cross compile for
s390.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 .shippable.yml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/.shippable.yml b/.shippable.yml
index 1a1fd7a91d..653bd750fe 100644
--- a/.shippable.yml
+++ b/.shippable.yml
@@ -5,6 +5,8 @@ env:
       TARGET_LIST=arm-softmmu,arm-linux-user
     - IMAGE=debian-arm64-cross
       TARGET_LIST=aarch64-softmmu,aarch64-linux-user
+    - IMAGE=debian-s390x-cross
+      TARGET_LIST=s390x-softmmu,s390x-linux-user
 build:
   pre_ci:
     - make docker-image-${IMAGE}
-- 
2.11.0