disallow parallel execution for spectator job

Author: zetroot

src/NTorSpectator.Observer/Program.cs

@@ -50,6 +50,7 @@
     var jobDetail = JobBuilder.Create<SpectatorJob>()
         .WithDescription("Tor spectator job")
         .WithIdentity("tor-spectator")
+        .DisallowConcurrentExecution()
         .Build();
     cfg.AddJob<SpectatorJob>(jobKey: jobDetail.Key, configure: j => {});
     cfg.AddTrigger(t => t.WithCronSchedule("0 0 * * * ?").ForJob(jobDetail));