We are currently sat on 4.12.4, but the latest stable today is 4.13.13. If we are tracking the latest stable at present, then we need to update to 4.13.13.

Longer term (pun intended), if we are going to track a longterm rather than a stable kernel version, then we probably want to wait for the next longterm (which is 4.14 iirc), which has only just been released, and thus will take a little while (a month or two?) to settle down into a longterm I think.