add test for multiwords typeKey

In https://github.com/emberjs/data/commit/766f0c9a8cdc8d21b99d80378c01678f8c404aa3 the typeKey normalization changed from `singularize(camelize)` to `camelize(singularize)`.
This breaks an edge case when I am defining a 'multiword uncountable' rule in the inflector.

cc/ @mixonic, @stefanpenner

Ultimately, @stefanpenner suggested to improve the inflector to take in account such a case.