Fixed behavior of `validates_numericality_of` validation `even` and `odd` options with not true values

Validation will look like:

    class Booking < ActiveRecord::Base
      validates :guests, numericality: { integer_only: true, even: :even_only?, greater_than: 1 }

      def even_only?; return true or false; end
    end

instead of:

    class Booking < ActiveRecord::Base
      validates :guests, numericality: { integer_only: true, greater_than: 1 }
      validates :guests, numericality: { even: true }, if: :even_only?

      def even_only?; return true or false; end
    end