Don't know how to build task 'backup:show_secrets'

I'm attempting to upgrade my Gitlab (with CI) to 8.0, using the migration guide here: http://doc.gitlab.com/ce/migrate_ci_to_ce/README.html, however when I reach the step about exporting the secret, I get the following:

root@grunt:~# gitlab-ci-rake backup:show_secrets
rake aborted!
Don't know how to build task 'backup:show_secrets'

(See full trace by running task with --trace)

I'm not sure where to go from here, so for now I'm rolling back.

root@grunt:~# gitlab-ci-rake env:info
/opt/gitlab/embedded/service/gem/ruby/2.1.0/bin/rake: No such file or directory - rvm

System information
Ubuntu
12.04
System:         unknown
Current User:   gitlab-ci
Using RVM:      no
Ruby Version:   2.1.6p336
Gem Version:    2.2.5
Bundler Version:1.5.3
Rake Version:   10.4.2
Sidekiq Version:2.17.0

GitLab CI information
Version:        8.0.0
Revision:       2c80e8f
Directory:      /opt/gitlab/embedded/service/gitlab-ci
DB Adapter:     postgresql

root@grunt:~# gitlab-rake gitlab:env:info

System information
System:         Ubuntu 12.04
Current User:   git
Using RVM:      no
Ruby Version:   2.1.6p336
Gem Version:    2.2.5
Bundler Version:1.5.3
Rake Version:   10.4.2
Sidekiq Version:3.3.0

GitLab information
Version:        8.0.0
Revision:       d70c051
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     postgresql
URL:            https://source.pinnsights.com
HTTP Clone URL: https://source.pinnsights.com/some-group/some-project.git
SSH Clone URL:  git@source.pinnsights.com:some-group/some-project.git
Using LDAP:     yes
Using Omniauth: no

GitLab Shell
Version:        2.6.5
Repositories:   /var/opt/gitlab/git-data/repositories
Hooks:          /opt/gitlab/embedded/service/gitlab-shell/hooks/
Git:            /opt/gitlab/embedded/bin/git