Fix intermittent spec failure

```
Failures:

  1) Mel::Progress .track tracks progress
     Failure/Error: _report.value.should eq(50)

       Expected: 50
            got: 80

     # spec/mel/progress_spec.cr:34
```

spec/support/config/worker.cr

@@ -1,6 +1,6 @@
 Mel.configure do |settings|
   settings.batch_size = -1
-  settings.poll_interval = 1.millisecond
+  settings.poll_interval = 10.milliseconds
   settings.redis_url = ENV["REDIS_URL"]
   settings.timezone = Time::Location.load("America/Los_Angeles")
 end