Add missing parameter on nicknamize method

Author: fblupi

decidim-core/app/forms/decidim/ephemeral_user_form.rb

@@ -16,7 +16,7 @@ def name
     end
 
     def nickname
-      super || User.nicknamize(name)
+      super || User.nicknamize(name, organization.id)
     end
   end
 end