Fix .gitlab-ci.yml to use gitlab-ci 0.8.0
The nix/ci.nix was updated to use gitlab-ci 0.8.0 with cachix enabled, but .gitlab-ci.yml was still pointing to 0.3.0. This caused cachix jobs not to run.
The nix/ci.nix was updated to use gitlab-ci 0.8.0 with cachix enabled, but .gitlab-ci.yml was still pointing to 0.3.0. This caused cachix jobs not to run.