Remove unwanted migration - rentalships rename

migration was failing attempting to rename rentals to rentals
assuming that rentals previously had the name rentships
Fix failing specs

* specs were created before date validation was added
* modified FactoryGirl.create(:rental) calls to avoid validation failures
Update rails to 3.2.15

* upgrades rails from 3.2.8 to 3.2.15
* contains many security fixes