Why Won't My Facebook Update
Edit: this seems to be a problem that Facebook understand. It's an issue with the Facebook application, and not a generalised Play Shop problem.
This is what benefited me at the very least.
- Settings > Applications > All > Google Play Store, Clear information and also Clear cache
- Settings > Apps > All > Google Play Solutions > Manage space, Clear all data as well as Clear cache
It doesn't hurt if you reboot your phone prior to you try updating facebook once again. And also, the set up was SLOW. Just a minimum of 4-5 mins. Yet, it did work. If not try to uninstall it, or merely await a solution.