when i test it , it has errors.

```
var natUpnp = require('nat-upnp');

var client = natUpnp.createClient();

client.portMapping({
public: 12345,
private: 54321,
ttl: 0
}, function(err) {
console.log(err)
// Will be called once finished
});
```
```

$ node pnp.js
Error: timeout
at Timeout._onTimeout (C:\Users\毛毛\Desktop\新建文件夹\node_modules\_nat-up
np@1.1.1@nat-upnp\lib\nat-upnp\client.js:187:14)
at ontimeout (timers.js:475:11)
at tryOnTimeout (timers.js:310:5)
at Timer.listOnTimeout (timers.js:270:5)
```

Reproduce the example from pnp.js with node and inspect the timeout at lib/nat-upnp/client.js:187. Check the reported UPnP port-mapping failure and surrounding client behavior; done means the cause is identified and the example either succeeds or reports the limitation clearly.

Written by the indexing model from the issue text.