74977456 'Articles model/controller/view specs refactoring'

https://www.pivotaltracker.com/story/show/74977456
(part of epic 74977456 https://www.pivotaltracker.com/epic/show/1288994)
replace double with FactoryGirl.build_stubbed or Article.new.
if you need friendly_id set, then also use allow(@article).to receive(:friendly_id)...