initialize() method only supports the "models" parameter as an array

In the [initialize](https://github.com/wyuenho/backbone-pageable/blob/master/lib/backbone-pageable.js#L283) method, the "models" parameter is considered an array. The thing is, in a plain backbone collection, I can do something like:
```javascript
var collection = new Backbone.Collection({hello: 'world'})
```
and it will instantiate the collection with a single model in it.

But if I do this with a pageable collection, I get errors because an object is not expected.