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)
```

1 files changed, 1 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/counter_cache.rb b/activerecord/lib/active_record/counter_cache.rb
index c654d4703a..f4ee008a12 100644
--- a/activerecord/lib/active_record/counter_cache.rb
+++ b/activerecord/lib/active_record/counter_cache.rb
@@ -105,7 +105,7 @@ module ActiveRecord
         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