Refactor DbFileBackend for Rails 4 AREL conformity

ActiveRecord#update_all was deprecated in Rails 2.3.8 and has since been replaced by ActiveRecord::Relation#update_all.  With this change the method signature (accepted parameters) and usage have also changed requiring the refactoring.
Refactor DbFileBackend to utilize hash rocket (i.e. =>) style delimiter

For backwards compatibility between older and newer Ruby versions.
Merge pull request #9 from corlissc/master

Refactor DbFileBackend for Rails 4 AREL conformity