Updated: rspec-rails from ~>4.0.0.beta2 to ~>6.0.0

[anitagraham]

Moved :it_has_behaviour alias to refinery's spec_helper, as it was being called from both images/spec and resources/spec.

Deprecate no more: Handling errors as objects now - when adding them (for image/resource validation), and when presenting them.

"The implicit block expectation syntax is deprecated" from refinery/images and refinery/resources. Added explicit block {} at expects where required, and de-lambda-ed the blocks being called.