Works around primary key being cast due to pluck bug

[butchmarshall]

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• Maintains compliance with JSON:API
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This fixes issue #1156 and provides a complete set of fixes for pull request #986.

[lgebhardt]

Thanks for the fix. Could you please rework the tests so this passes on rails 4.2?

[butchmarshall]

Can do. It may take me a day or so but it'll definitely get done. Thanks!

[butchmarshall]

Looks like it's failing because I added a key_type :uuid JSONAPI::Resource test (none had existed before).

Most likely related to rails/rails#24857

Workaround is to set self.primary_key = "id" on the resource.

I've pushed a fix (note my commenting out of the final assert_equal in my new test)

[lgebhardt]

@butchmarshall Thanks for tracking that down and fixing!