The Facebook app for Windows Phone 8.1 looks to be receiving an update, though it's not entirely clear what's new. It's likely that the update simply includes some performance improvements and bug fixes, which are honestly never a bad thing.
If you're interested in version numbers, this update bumps the app up to version 220.127.116.11. As for those running Windows 10 Mobile, it doesn't look like an update is being pushed out to that version of the app — but we'll keep an eye out. In any case, you can download the update via the Windows Store link below, and shout out in the comments if you spot anything notable that we missed.