This currently causes things like:

```
Notice: /Stage[main]/Ruby/Ruby::Plugin[rbenv-default-gems]/Repository[/opt/boxen/rbenv/plugins/rbenv-default-gems]/ensure: current_value present, should be v1.0.0 (noop)
Notice: /Stage[main]/Ruby/Ruby::Plugin[rbenv-gem-rehash]/Repository[/opt/boxen/rbenv/plugins/rbenv-gem-rehash]/ensure: current_value present, should be v1.0.0 (noop)
```

/cc @jfryman @rodjek