Facebook App Won't Update
Edit: this appears to be a problem that Facebook recognize. It's a problem with the Facebook application, and not a generalised Play Shop concern.
This is what benefited me at least.
- Settings > Apps > All > Google Play Shop, Clear data and also Clear cache
- Settings > Applications > All > Google Play Solutions > Manage room, Clear all information as well as Clear cache
It doesn't harmed if you reboot your phone prior to you attempt updating facebook once again. And, the install was SLOW. Simply at least 4-5 mins. But, it did work. If not attempt to uninstall it, or just wait for a fix.