Incorrectly calling _split_options on something that isn't a dictionary

This is the correct fix for the exception in issue #13.  The higher level issue in pyactiveresource needs to be fixed elsewhere.

The ShopifyResource class calls the ActiveResource method _split_options and passes something that isn't a dictionary. This causes the exception.


ActiveResource _update correctly checks that the attributes are a dictionary. I've added the same check to ShopifyResource.