implement rspec for assign_category() and add_or_update_price() of AppItem
implement spec for add_or_update_description
implement spec for add_or_update_device
implement spec for add_or_update_ratings
implement spec for new_or_update_publisher
add simple-cov
implement rspec for Country.own?, AppItem.load_google_play and AppItem.add_or_update_attributes
implement some specs for Ranking method
implement rspec for AppItem.updatable?
refactor AppItem and Ranking
remove :foreign_key
remove DEPRECATION WARNING
Merge pull request #7 from ryysd/write_rspec

Write rspec