Removed "on" prefix when describing events
Removed "on" prefix when describing events

Per issue #214, removed what I believe to be the last instance of "on"
prefixing an event name.

chadoliver/ServiceWorker,karolklp/ServiceWorker,slightlyoff/ServiceWorker,zuzusik/ServiceWorker,mkruisselbrink/ServiceWorker,slightlyoff/ServiceWorker,zuzusik/ServiceWorker,justinleoye/ServiceWorker,karolklp/ServiceWorker,mkruisselbrink/ServiceWorker,justinleoye/ServiceWorker,martinthomson/ServiceWorker,zuzusik/ServiceWorker,chadoliver/ServiceWorker,justinleoye/ServiceWorker,martinthomson/ServiceWorker,karolklp/ServiceWorker,martinthomson/ServiceWorker,chadoliver/ServiceWorker