$ plugn install github.com/progrium/some-plugin # install master
$ plugn update some-plugin v1 # pins to the v1 tag (or branch!)
$ plugn update some-plugin # no-op since v1 is a tag, but otherwise pulls current branch
$ plugn update some-plugin v2 # upgrade to v2 when released
$ plugn update some-plugin v1 # rollback to v1 cause v2 sucked
comments welcomed!
requirements from #8
fixes #8 refs: progrium/dokku#1531