Depends on github.com/docker-infra/docker-backup/backup that doesn't actually exist

[calmh]

This somewhat cryptic error:

jb@syno:~ $ go get github.com/discordianfish/docker-backup
# cd .; git clone https://github.com/docker-infra/docker-backup /Users/jb/src/github.com/docker-infra/docker-backup
Cloning into '/Users/jb/src/github.com/docker-infra/docker-backup'...
fatal: could not read Username for 'https://github.com': terminal prompts disabled
package github.com/docker-infra/docker-backup/backup: exit status 128

Is caused by github.com/docker-infra/docker-backup being a 404.