Doc fix [ci skip]

activerecord/lib/active_record/associations/through_association.rb

@@ -33,7 +33,7 @@ def target_scope
         # Construct attributes for :through pointing to owner and associate. This is used by the
         # methods which create and delete records on the association.
         #
-        # We only support indirectly modifying through associations which has a belongs_to source.
+        # We only support indirectly modifying through associations which have a belongs_to source.
         # This is the "has_many :tags, through: :taggings" situation, where the join model
         # typically has a belongs_to on both side. In other words, associations which could also
         # be represented as has_and_belongs_to_many associations.