Fix cache secret name key typos

this typo caused the following bug

 volumes for pod "gitlab-runner-gitlab-runner-6d775d6966-msfpr_gitlab(c30f1f1b-67f2-11e8-bb0c-42010a840094)": timeout expired waiting for volumes to attach or mount for pod "gitlab"/"gitlab-runner-gitlab-runner-6d775d6966-msfpr". list of unmounted volumes=[init-runner-secrets]. list of unattached volumes=[runner-secrets etc-gitlab-runner init-runner-secrets scripts default-token-xjrbr]