Fix using Struct

`Struct.new` returns a class. Inheritance isn't required.

```
class NewsletterJob < Struct.new(:text, :emails)
  def perform
  end
end

NewsletterJob.superclass # => #<Class:0x007ffa829adad8>
NewsletterJob.superclass.superclass # => Struct

Test = Struct.new(:foo) do
  def perform
  end
end
Test.superclass # => Struct
```