Shortcodes / Facebook: update regex to support valid Facebook content URLs

The regular expression here is updated to support valid Facebook URLs that can be embedded, such as:

https://www.facebook.com/TheAcademy/photos/a.212963591405.141172.83574526405/10152040500621406
https://www.facebook.com/115099421882868/photos/a.116098101783000.15816.115099421882868/655027811223357/?type=1
https://www.facebook.com/ellentv/photos/a.182755292239.124686.26012002239/10152299789332240/?type=1