Fix update counters of multiple records with touch: true

Currently does not work the following example in the doc:

```ruby
  # For the Posts with id of 10 and 15, increment the comment_count by 1
  # and update the updated_at value for each counter.
  Post.update_counters [10, 15], comment_count: 1, touch: true
  # Executes the following SQL:
  # UPDATE posts
  #    SET comment_count = COALESCE(comment_count, 0) + 1,
  #    `updated_at` = '2016-10-13T09:59:23-05:00'
  #  WHERE id IN (10, 15)
```

Author: kamipo

activerecord/lib/active_record/counter_cache.rb

@@ -105,7 +105,7 @@ def update_counters(id, counters)
         end
 
         if touch
-          object = find(id)
+          object = find(id.is_a?(Array) ? id.first : id)
           updates << object.class.send(:sanitize_sql_for_assignment, touch_updates(object, touch))
         end
 

activerecord/test/cases/counter_cache_test.rb

@@ -227,6 +227,16 @@ class ::SpecialReply < ::Reply
     end
   end
 
+  test "update counters of multiple records with touch: true" do
+    t1, t2 = topics(:first, :second)
+
+    assert_touching t1, :updated_at do
+      assert_difference ["t1.reload.replies_count", "t2.reload.replies_count"], 2 do
+        Topic.update_counters([t1.id, t2.id], replies_count: 2, touch: true)
+      end
+    end
+  end
+
   test "update multiple counters with touch: true" do
     assert_touching @topic, :updated_at do
       Topic.update_counters(@topic.id, replies_count: 2, unique_replies_count: 2, touch: true)