gitlab-ci: apt upgrade so that tests run with current updates

The MD5 signature stuff was failing in tests because the CI image was
using a quite old version of Java's jarsigner, which had not yet disabled
MD5.

.gitlab-ci.yml

@@ -2,6 +2,7 @@ image: registry.gitlab.com/fdroid/ci-images:server-latest
 
 test:
   script:
+    - apt-get -qq update && apt-get -y dist-upgrade
     - mkdir -p /usr/lib/python3.4/site-packages/
     # workaround https://github.com/pypa/setuptools/issues/937
     - pip3 install setuptools==33.1.1