Update part-4.md
Update part-4.md

change from 
var Event = keystone.List('Event'); 
to 
var Event = keystone.list('Event');
Pop-Code/keystone,Pop-Code/keystone,matthewstyers/keystone,frontyard/keystone,matthewstyers/keystone,matthewstyers/keystone,frontyard/keystone,frontyard/keystone