originateTimestamp equals 0 in returned packet

Dieses Issue hat noch niemand übernommen.

Running the slightly modified example

```js
const ntp = require('..');

ntp(function(err, response){
if(err) return console.error(err);
console.log(response);
});
```

`originateTimestamp === 0` is returned which renders roundtrip delay `d` and system clock offset `t` unusable.

```js
Packet {
leapIndicator: 0,
version: 4,
mode: 4,
stratum: 2,
pollInterval: 6,
precision: 233,
referenceIdentifier: ,
referenceTimestamp: 1577013057260.7312,
originateTimestamp: 0,
receiveTimestamp: 1577013390216.6448,
transmitTimestamp: 1577013390216.6702,
rootDelay: ,
rootDispersion: ,
destinationTimestamp: 1577013390262,
time: 2019-12-22T11:16:30.216Z,
d: 1577013390261.9746,
t: 788506695085.6575
}
```

According to https://tools.ietf.org/html/rfc2030#section-6

> In unicast and anycast modes, the Receive Timestamp and Transmit Timestamp
> fields are set to the time of day when the message is sent and the
> Originate Timestamp field is copied unchanged from the Transmit
> Timestamp field of the request. It is important that this field be
> copied intact, as a NTP client uses it to avoid replays. In multicast
> mode, the Originate Timestamp and Receive Timestamp fields are set to
> 0 and the Transmit Timestamp field is set to the time of day when the
> message is sent.

I suppose that client and server operate in unicast/ anycast mode. If this is the case I would like to change:

```diff
--- a/index.js
+++ b/index.js
@@ -63,7 +63,7 @@ NTP.prototype.time = function (callback) {
NTP.createPacket = function () {
const packet = new Packet();
packet.mode = Packet.MODES.CLIENT;
- packet.originateTimestamp = Date.now();
+ packet.transmitTimestamp = Date.now();
return packet.toBuffer();
};
```

Beginne in index.js bei NTP.createPacket und reproduziere das Problem mit dem im Bericht gezeigten Beispiel. Vergleiche das konstruierte Paket mit dem zitierten Verhalten gemäß RFC 2030 und überprüfe anschließend, dass die zurückgegebenen Zeitstempel die Roundtrip-Verzögerung und den Offset der Systemuhr nutzbar machen.

Vom Indexierungsmodell aus dem Issue-Text verfasst.