fix comment

README.md

@@ -1033,7 +1033,7 @@ doc.transact(() => {
   ytext.insert(0, 'abc')
 }, 41)
 undoManager.undo()
-ytext.toString() // => '' (not tracked because 41 is not an instance of
+ytext.toString() // => 'abc' (not tracked because 41 is not an instance of
                  //        `trackedTransactionorigins`)
 ytext.delete(0, 3) // revert change