This fixes the following warning when creating your own transformer like so:

```ruby
class SomeTransformer
  def call(node:, **_)
    {
      node_allowlist: [node],
    }
  end
end
```

```
/usr/local/bundle/ruby/2.7.0/gems/sanitize-5.2.1/lib/sanitize.rb:207: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
```