Fix single link which now expects Url object

As [Switch Drupal::l() and LinkGenerator to expect a Url object](https://www.drupal.org/node/2277103) is in place, current code produces fatal error. In this commit is a simple fix.
That's not completely correct, Drupal::l() only has two arguments, the title and the Url object. array() can be left out, $options need to be set on the url object, you can do it inline like Url::fromRoute('token.tree')->setOptions(...), as setOptions() return $this.