[403] Allows foreign key to_sym on Array

[julienemo]

This is not my original idea !!!!
MadBomber had this idea and personnally it helped me. I thought I might just as well make a PR

Original issue here
#403

[panteo]

Can someone merge this PR please?

[panteo]

It can also be implemented like this:

      def foreign_key?
        @domain.relationships_by_entity_name(@model.name).map(&:associations).flatten.map { |associaton|
          [associaton.send(Domain.foreign_key_method_name)].flatten.map(&:to_sym).join("_")
        }.include?(name.to_sym)
      end