Add transation to onupgradeneeded event target

See http://stackoverflow.com/questions/16563562/indexeddb-handle-data-migration-onupgradeneeded for example of this behavior. Mozilla documentaion call them change transactions https://developer.mozilla.org/en-US/docs/Web/API/IDBDatabase , so there might be a difference but at least this makes my code work which covers a lot of the IndexedDB api. I will do more tests with indexes.