Remove duplicated code

Author: johnnyshields

lib/mongoid/touchable.rb

@@ -27,10 +27,7 @@ def touch(field = nil)
         return false if _root.new_record?
 
         touches = __gather_touch_updates(Time.now, field)
-        unless touches.blank?
-          selector = _root.atomic_selector
-          _root.collection.find(selector).update_one(positionally(selector, '$set' => touches), session: _session)
-        end
+        _root.send(:persist_atomic_operations, '$set' => touches) if touches.present?
 
         __run_touch_callbacks_from_root
         true