"-reverse" in sort_by applies to entire list only

[ayunami2000]

https://github.com/iv-org/instances.invidio.us/blob/master/src/instances.cr#L169

suggestion (fix?): make it so that e.g. ?sort_by=health,users-reverse lists them first by health and then by least users (right now it lists them first by health and then by users and then reverses the entire list)