Return `id` assumption for simple polymorphic `Collection#model` factories.

Also, add tests to make sure it doesn't break in the future.
Make new tests more thorough
remove un-used local variables
Merge pull request #3053 from sfishel18/master

Remove un-used local variables
Update devDependencies

PhantomJS fixed the really annoying "CoreText performance note:" message in
1.9.3 or so.
Merge pull request #3054 from caseywebdev/deps

Update devDependencies