Fix missing Location header in 0.9.x (#1362)

* Add failing test to demonstrate regression

It looks like this test was originally added as part of the Location
header work, but was subsequently removed.

See: cerebris/jsonapi-resources@933750c

* Fix location header to be set correctly, fixes #1361

Previously, a change had been make to use string keys instead of symbol keys, see
cerebris/jsonapi-resources@010f024

The change did not update how the location header was set to also use string keys.

This PR resolves the issue by also using a string key.

Author: paulspringett

lib/jsonapi/acts_as_resource_controller.rb

@@ -234,7 +234,7 @@ def render_results(operation_results)
         render_options[:body] = JSON.generate(content)
       end
 
-      render_options[:location] = content[:data]["links"][:self] if (
+      render_options[:location] = content[:data]["links"]["self"] if (
         response_doc.status == :created && content[:data].class != Array && content[:data]["links"]
       )
 

test/controllers/controller_test.rb

@@ -591,6 +591,7 @@ def test_create_simple
     assert_equal 'JR is Great', json_response['data']['attributes']['title']
     assert_equal 'JSONAPIResources is the greatest thing since unsliced bread.', json_response['data']['attributes']['body']
     assert_equal "http://test.host/posts/#{json_response['data']['id']}", json_response['data']['links']['self']
+    assert_equal json_response['data']['links']['self'], response.location
   end
 
   def test_create_simple_id_not_allowed