Uninstall Ruby 2.1.2
Uninstall Ruby 2.1.2

The last app to use this version was manuals-publisher which was recently
upgraded to 2.2.4 (see: https://github.com/alphagov/manuals-publisher/pull/806).

This was verified with:

    fab production puppet_class:govuk_rbenv::all rbenv.version_in_use:2.1.2
    fab staging puppet_class:govuk_rbenv::all rbenv.version_in_use:2.1.2
    fab integration puppet_class:govuk_rbenv::all rbenv.version_in_use:2.1.2

All of which reported back a clean slate.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet