using with the cluster is not working
Hello!

How are you?

I have an example:

```js
        const options = {
            key: certKey,
            cert: cert,
        };

        // native nodejs 9.11.1
        const http2 = require('http2')
        http2.createSecureServer(options, this.app.callback()).listen(p3x.npm.conf.web.port, (err) => {
            if (err) {
                return reject(err);
            }
            console.log(`Web listening on port ${p3x.npm.conf.web.port}`);
            resolve();
        });
```

What is weird, is that with ```Express``` it is working right away:
```text
Apr 16 18:05:07 server boot[14710]: [2018/04/16 18:05:07.233] [LOG]   [WORKER 005] [PID: 14733] [CORE] [SERVICE] [EXPRESS] 2001:470:1f1b:5b5:691b:cb3:6880:8159 200 GET /favicon.ico 2ms Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36
Apr 16 18:05:07 server boot[14710]: [2018/04/16 18:05:07.363] [LOG]   [WORKER 003] [PID: 14722] [CORE] [SERVICE] [EXPRESS] 2001:470:1f1b:5b5:691b:cb3:6880:8159 200 GET /api/core/util/random/32 2ms Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36
Apr 16 18:05:07 server boot[14710]: [2018/04/16 18:05:07.389] [LOG]   [WORKER 004] [PID: 14727] [CORE] [SERVICE] [EXPRESS] 2001:470:1f1b:5b5:691b:cb3:6880:8159 200 GET /favicon.ico 2ms Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36
Apr 16 18:05:07 server boot[14710]: [2018/04/16 18:05:07.501] [LOG]   [WORKER 002] [PID: 14721] [CORE] [SERVICE] [EXPRESS] 2001:470:1f1b:5b5:691b:cb3:6880:8159 200 GET /api/core/util/random/32 2ms Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36
Apr 16 18:05:07 server boot[14710]: [2018/04/16 18:05:07.528] [LOG]   [WORKER 005] [PID: 14733] [CORE] [SERVICE] [EXPRESS] 2001:470:1f1b:5b5:691b:cb3:6880:8159 200 GET /favicon.ico 2ms Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36
Apr 16 18:05:07 server boot[14710]: [2018/04/16 18:05:07.655] [LOG]   [WORKER 003] [PID: 14722] [CORE] [SERVICE] [EXPRESS] 2001:470:1f1b:5b5:691b:cb3:6880:8159 200 GET /api/core/util/random/32 1ms Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36
Apr 16 18:05:07 server boot[14710]: [2018/04/16 18:05:07.681] [LOG]   [WORKER 004] [PID: 14727] [CORE] [SERVICE] [EXPRESS] 2001:470:1f1b:5b5:691b:cb3:6880:8159 200 GET /favicon.ico 2ms Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36
```

But when I use ```Koa``` it only works with a different browser and is stuck, with using the last used worker:

```Chrome```  : 
```text
2018/04/16 18:05:57.418 [LOG]   [WORKER 0004] [PID: 008599] GET / - 0ms
2018/04/16 18:05:57.479 [LOG]   [WORKER 0004] [PID: 008599] GET /favicon.ico - 0ms
2018/04/16 18:05:58.866 [LOG]   [WORKER 0004] [PID: 008599] GET / - 0ms
2018/04/16 18:05:58.893 [LOG]   [WORKER 0004] [PID: 008599] GET /favicon.ico - 1ms
2018/04/16 18:05:59.035 [LOG]   [WORKER 0004] [PID: 008599] GET / - 0ms
2018/04/16 18:05:59.060 [LOG]   [WORKER 0004] [PID: 008599] GET /favicon.ico - 0ms
2018/04/16 18:05:59.186 [LOG]   [WORKER 0004] [PID: 008599] GET / - 0ms
2018/04/16 18:05:59.210 [LOG]   [WORKER 0004] [PID: 008599] GET /favicon.ico - 0ms
2018/04/16 18:05:59.440 [LOG]   [WORKER 0004] [PID: 008599] GET / - 0ms
2018/04/16 18:05:59.465 [LOG]   [WORKER 0004] [PID: 008599] GET /favicon.ico - 0ms
2018/04/16 18:05:59.576 [LOG]   [WORKER 0004] [PID: 008599] GET / - 0ms
2018/04/16 18:05:59.601 [LOG]   [WORKER 0004] [PID: 008599] GET /favicon.ico - 0ms
```

```Firefox``` : 

```text
2018/04/16 18:05:51.316 [LOG]   [WORKER 0008] [PID: 008643] GET / - 1ms
2018/04/16 18:05:51.682 [LOG]   [WORKER 0008] [PID: 008643] GET / - 0ms
2018/04/16 18:05:51.881 [LOG]   [WORKER 0008] [PID: 008643] GET / - 0ms
2018/04/16 18:05:52.022 [LOG]   [WORKER 0008] [PID: 008643] GET / - 0ms
2018/04/16 18:05:52.193 [LOG]   [WORKER 0008] [PID: 008643] GET / - 0ms
2018/04/16 18:05:52.295 [LOG]   [WORKER 0008] [PID: 008643] GET / - 0ms
2018/04/16 18:05:52.434 [LOG]   [WORKER 0008] [PID: 008643] GET / - 0ms
2018/04/16 18:05:52.596 [LOG]   [WORKER 0008] [PID: 008643] GET / - 0ms
2018/04/16 18:05:52.734 [LOG]   [WORKER 0008] [PID: 008643] GET / - 0ms
2018/04/16 18:05:52.825 [LOG]   [WORKER 0008] [PID: 008643] GET / - 0ms
2018/04/16 18:05:52.997 [LOG]   [WORKER 0008] [PID: 008643] GET / - 0ms
2018/04/16 18:05:53.120 [LOG]   [WORKER 0008] [PID: 008643] GET / - 0ms
```

Do  you have an idea, why it is happening?