Correction to translation of EnumStrings in rich_types.rdoctest

In Hobo's <input> tag definition for EnumString, Hobo simply tacks on an "s" to pluralize the field name:

```
    [I18n.t("activerecord.attributes.#{this_parent.class.to_s.downcase}/#{this_field}s.#{v}",
      :default => default),
    v]
```

For the example shown in the documentation, "statuses" was not correct. Hobo actually looks for "statuss", oddly enough. 

Tim