Basic Demo - suggested update

In the basic demo there is a millisecond drift in the output.
I think changing the code like so gives output every 1000ms rather than 1001ms

```
void loop() {
    static int last = 0;

    if ((millis () - last) **>=** SHOW_TIME_PERIOD) {
        last = millis ();
        Serial.println (NTP.getTimeDateStringUs ());
    }
}
```