update method
Persists an updated job and returns it.
Implementation
@override
Future<RenderJob> update(RenderJob job) async {
await dir.create(recursive: true);
final temp = File('${_fileFor(job.id).path}.tmp');
await temp.writeAsString(jsonEncode(_encode(job)));
await temp.rename(_fileFor(job.id).path);
return job;
}