updated UPGRADE.md
updated UPGRADE.md

Changed ilios2->3 database migration filename to match the new one.
dartajax/ilios,stopfstedt/ilios,justinchu17/ilios,ilios/ilios,justinchu17/ilios,justinchu17/ilios,thecoolestguy/ilios,Trott/ilios,thecoolestguy/ilios,stopfstedt/ilios,Trott/ilios,dartajax/ilios,justinchu17/ilios,ilios/ilios