locking_enabled? now returns boolean

updated locking_enabled? to keep consistent with [documentation](http://api.rubyonrails.org/classes/ActiveRecord/Locking/Optimistic/ClassMethods.html#method-i-locking_enabled-3F)

Currently locking_enabled? returns a database column object. 

This is my first commit so I apologize in advance if I've failed to follow the contributing guidelines in any way.