Add jsonapi rspec helper gem

[zakariaf]

Add jsonapi-rspec which provides some beautiful RSpec matchers for JSON API

Some of the matchers:

Available matchers:

expect(document['data']).to have_id('12')
expect(document['data']).to have_type('users')
expect(document['data']).to have_jsonapi_attributes(:name, :email)
expect(document['data']).to have_jsonapi_attributes(:name, :email, :country).exactly
expect(document['data']).to have_attribute(:name).with_value('Lucas')
expect(document['data']).to have_relationships(:posts, :comments)

Check the gem GitHub page to see the list of all RSpec matchers