i'm too lazy to go look
but if there are serious bug fixes or something else important sounding probably,is there any new functionality that sounds useful?
since the firmware upgrade is something that if it goes wrong can leave you with a brick it is not to be done just cause you have nothing better to do
if you do decide to upgrade only upgrade from a wired connection and disconnect the wan cable and other wireless clients ideally have it and the upgrading pc on a battery back up... a power outage mid flash is a awesome way to end up with a brick. make sure you read (twice) and understand the process before beginning and ideally have another way to get online to seek info should something go wrong.
but if it isn't fixing security flaws or some other compelling reason to upgrade and it is working good it might well be fine to just leave it be.
i can say from experience (my old linksys router semi bricked itself on a firmware upgrade) it is a good idea to see what the bad flash recovery process looks like / what the bad flash recovery options are BEFORE attempting the flash.