add test for no attribute type

from http://emberjs.com/guides/models/defining-models/:
"If you don't specify the type of the attribute, it will be whatever was
provided by the server. You can make sure that an attribute is always
coerced into a particular type by passing a type to attr:"
Merge pull request #2522 from kellyselden/add-no-attribute-type-test

add test for no attribute type