mongoid - scope by state should query by state_column field

[lucasrenan]

this problem occurs when change the default state column field ("state") and tries to query by state name

stateflow do
    state_column :status
    initial :draft

    state :draft
    state :published
end

MyModel.published

=> #<Mongoid::Criteria
  selector: {:state=>"published"},
  options:  {},
  class:    Dealer,
  embedded: false>

https://github.com/lucasrenan/stateflow/blob/master/lib/stateflow/persistence/mongoid.rb#L12

I'm planning to send a pull request soon.