Corrects environment and failing tests

[nachocodoner]

Corrects "Respect idAttribute" and "Remove duplicate models" tests
Corrects "Collections handle duplicates correctly" test
Updates deprecated browserify version

New versions of Backbone take up changes that affects to Supermodel library.

Collections are no longer going to merge attributes from duplicate models inside a collection. Instead, and for fixing the "Collections handle duplicates correctly" test, you have to pass an option specifically ({merge: true}).

Regarding "Respect idAttribute" test, Collections now require the model constructor passed as a parameter to take advantage of the specific model context, for example, to be able to get a model from a collection by the custom idAttribute definition. Thus, the collection associated for each particular model constructor (all) must be defined in such a way.

Finally, the "Remove duplicate models" test got failed in the last Backbone version (1.2.1) as a regression bug was created (jashkenas/backbone#3693). For the moment, the Backbone version defined at the package has been limited by versions prior to 1.2.1 version, until it is fixed.

[TheBox193]

Nice 👍

[flippyhead]

Fantastic thank you!