gitlab-ci: install zip

The dist-zip automake option requires this package.

.gitlab-ci.yml

@@ -6,7 +6,7 @@ build:
   before_script:
     - apt-get update &&
       apt-get install -y libogg-dev libvorbis-dev libao-dev
-        gettext
+        gettext zip
   script:
     - ./autogen.sh
     - ./configure