remove outdated Y instance in comments

src/utils/Transaction.js

@@ -28,7 +28,8 @@ import { callAll } from 'lib0/function'
  * possible. Here is an example to illustrate the advantages of bundling:
  *
  * @example
- * const map = y.define('map', YMap)
+ * const ydoc = new Y.Doc()
+ * const map = ydoc.getMap('map')
  * // Log content when change is triggered
  * map.observe(() => {
  *   console.log('change triggered')
@@ -37,7 +38,7 @@ import { callAll } from 'lib0/function'
  * map.set('a', 0) // => "change triggered"
  * map.set('b', 0) // => "change triggered"
  * // When put in a transaction, it will trigger the log after the transaction:
- * y.transact(() => {
+ * ydoc.transact(() => {
  *   map.set('a', 1)
  *   map.set('b', 1)
  * }) // => "change triggered"