docker-cleanup: fix untagged_containers after d5868e8
docker-cleanup: fix untagged_containers after d5868e8

Also adds `tail -n +2`. Thanks @thomassuckow.

blueyed/dotfiles,scorpiovn/dotfiles,scorpiovn/dotfiles,blueyed/dotfiles,blueyed/dotfiles,scorpiovn/dotfiles,blueyed/dotfiles,blueyed/dotfiles,scorpiovn/dotfiles,scorpiovn/dotfiles