Update Model.dump to first load the value

Update Model.dump to first load the value to ensure it's the correct type.
so, shouldn't the method return what the media_type expects? i.e. a Struct-like object?
In other words, it seems to me that perhaps, instead of:

```ruby
      def timestamps
        {
          stranded_at: stranded_at,
          pending_at: pending_at,
          booted_at: booted_at,
          operational_at: operational_at,
          terminated_at: terminated_at
        }
      end
```

it should return a model:

```ruby
      def timestamps
        Model.new {
          stranded_at: stranded_at,
          pending_at: pending_at,
          booted_at: booted_at,
          operational_at: operational_at,
          terminated_at: terminated_at
        }
      end
```

thoughts?

(Another story to discuss is the actual error that right now might be returned...etc...)