use sort_by

activerecord/lib/active_record/associations/class_methods/join_dependency.rb

@@ -151,7 +151,7 @@ def build(associations, parent = nil, join_type = Arel::InnerJoin)
               build(association, parent, join_type)
             end
           when Hash
-            associations.keys.sort{|a,b|a.to_s<=>b.to_s}.each do |name|
+            associations.keys.sort_by { |a| a.to_s }.each do |name|
               join_association = build(name, parent, join_type)
               build(associations[name], join_association, join_type)
             end