Update syn transaction example

[fboucquez]

This one seems out of date with the hardcoded values.

https://docs.symbolplatform.com/guides/monitor/turning-the-asynchronous-transaction-announcement-into-synchronous.html#turning-the-asynchronous-transaction-announcement-into-synchronous

Also, the transaction service is not used correctly. It's a lot simpler:

await listener.open()
try{
  const transaction = await transactionService.announce(signedTransaction, listener).toPromise() 
  console.log(transaction);
} catch(e){
  console.error(e)
} finally{
  listener.close()
}

[fboucquez]

The hardcoded values should be fixed in #551. The service example would need to be updated