As per the support ticket I raised, ActiveSupport as of at least 3.2 (I haven't looked at 3.1) no longer has the core extension Module#attr_accessor_with_default. I've replaced it with a plain ruby equivalent and removed the dependency.
Remove dependency on attr_accessor_with_default
attr_accessor_with_default has been removed from ActiveSupport 3.2,
breaking the lighthouse-api gem when used with newer projects. This
patch reimplements the behaviour without external dependencies.