Make compatible with Backbone 0.9.9 (collection.fetch changes)

related: https://github.com/documentcloud/backbone/pull/1975
Update unit tests to pass with latest Backbone changes
bumping infiniScroll version and putting latest version of backbone and underscore in spec/vendor
Fix typo in docs
Merge pull request #8 from philfreo/patch-1

Make compatible with Backbone 0.9.9 (collection.fetch changes)