Fixes has_many conditions in Rails 4.1

Rails 4.1 passes the association into the scope lambda, not the class.
Rather, the associated object's class is available within the context
of the lambda as `model`.
Update contributors on README [ci skip]
Add spec validating sort order of versions association by default
Merge pull request #373 from patbenatar/fix/rails-4.1-has-many-association

Fixes has_many conditions in Rails 4.1
Update CHANGELOG [ci skip]
Update specs checking for truthiness and falseyness to use syntax avoiding RSpec deprecation warnings [ci skip]