.gitlab-ci.yml: Use /cache to put all contents
This is how a runner looks like:
$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/docker-252:1-262208-36eaa91b86966a7afa39fbdbe717bdec58bc10efc52e09accd3e8e9ee4038658 10G 144M 9.9G 2% /
tmpfs 3.9G 0 3.9G 0% /dev
tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup
/dev/vda1 79G 1.2G 75G 2% /cache
shm 64M 0 64M 0% /dev/shm
Edited by Javier Jardón