Add Debian Jessie build image

This image is meant to be used to build packages for the Jessie release of Debian. See debian/nginx-build.

.gitlab-ci.yml

@@ -63,6 +63,7 @@ lint-debian-jessie-build-script:
   stage: test
   image: debian:latest
   before_script:
+    - apt-get update
     - apt-get install -y shellcheck
   script:
     - shellcheck ./debian/jessie/setup.sh