[DependencyInjection] Added trailing commas

Taking int account @fabpto's comments:
* https://github.com/gnugat/symfony/commit/f9463daf2806e53b546f6c5c27e29e252c878a81#commitcomment-3784007
* https://github.com/gnugat/symfony/commit/f9463daf2806e53b546f6c5c27e29e252c878a81#commitcomment-3784010