Destroy function is broken for Backbone v1.0.0

[Edgar Rodriguez]

When destroying models the library is broken using Backbone v1.0.0. The method map does not contain a 'destroy' key anymore (see https://github.com/documentcloud/backbone/blob/master/backbone.js#L1194), so backbone doesn't find the correct http method to execute in https://github.com/documentcloud/backbone/blob/master/backbone.js#L1131

Submitting a pull request to fix this.