Rely on ActiveRecord.version. Is in support AR versions

see e.g.
https://github.com/rails/rails/blob/4-0-stable/activerecord/lib/active_record/version.rb

lib/ranked-model.rb

@@ -46,7 +46,7 @@ def handle_ranking_failure(ranker, ranking_failed_reason)
     abort_handle_ranking
   end
 
-  if defined?(Rails) && Rails.version >= '5'
+  if defined?(ActiveRecord) && ::ActiveRecord.version.to_s >= '5'
     def abort_handle_ranking
       throw :abort
     end