Reporting open port when using a non existing domain

This reports an open port for the non existent domain:
```
import NetMap from 'netmap.js'

const netmap = new NetMap()
const hosts = ['nonexistentdomain.com']
const ports = [80]

netmap.tcpScan(hosts, ports).then(results => {
  console.log(results)
})
```

I guess the DNS failure makes the delta to be similar to an open port.