README: removed the bash instruction from code blocks to fix markdown rendering at index.docker.io
README: removed the bash instruction from code blocks to fix markdown rendering at index.docker.io

outcoldman/docker-gitlab-ci,sameersbn/docker-gitlab-ci,outcoldman/docker-gitlab-ci,sameersbn/docker-gitlab-ci,bboehmke/docker-gitlab-ci,youhong316/docker-gitlab-ci,adiferd/docker-gitlab-ci,adiferd/docker-gitlab-ci,bboehmke/docker-gitlab-ci,youhong316/docker-gitlab-ci