ActiveRecord::Enum matcher

Hi guys,

I started a matcher for the  [ActiveRecord::Enum](http://edgeapi.rubyonrails.org/classes/ActiveRecord/Enum.html). I know we can`t merge this now since no released rails 4.1.0.

I only want to show you guys the idea =) and ask one thing: ActiveRecord::Enum is only on rails 4.1.0, how we can skip this specs in older rails versions?
We don't like statement modifiers as they are easy to miss when reading the code. Would you mind changing this to

```
if @options[:expected_enum_values]
  desc << " with #{@options[:expected_enum_values]}"
end
```

(adding a line break before and after)