Merge pull request #10049 from vipulnsward/optimize_around_merge_v1

optimize some code around merge

activerecord/lib/active_record/associations/through_association.rb

@@ -14,7 +14,7 @@ module ThroughAssociation #:nodoc:
         def target_scope
           scope = super
           chain[1..-1].each do |reflection|
-            scope = scope.merge(
+            scope.merge!(
               reflection.klass.all.with_default_scope.
                 except(:select, :create_with, :includes, :preload, :joins, :eager_load)
             )