Fix address of NTP server in example

For some reason the example failed to get a response from the IP address of `time.nist.gov`. I also didn't get a ping reply from that address to my laptop.
I had more luck with one of the servers of `pool.ntp.org`.
For the record I'm located in Amsterdam, Netherlands. Does this new address work in US and other parts of the world?

examples/WiFiUdpNtpClient/WiFiUdpNtpClient.ino

@@ -28,11 +28,11 @@ int keyIndex = 0;            // your network key index number (needed only for W
 
 unsigned int localPort = 2390;      // local port to listen for UDP packets
 
-IPAddress timeServer(129, 6, 15, 28); // time.nist.gov NTP server
+IPAddress timeServer(162, 159, 200, 123); // pool.ntp.org NTP server
 
 const int NTP_PACKET_SIZE = 48; // NTP timestamp is in the first 48 bytes of the message
 
-byte packetBuffer[ NTP_PACKET_SIZE]; //buffer to hold incoming and outgoing packets
+byte packetBuffer[NTP_PACKET_SIZE]; //buffer to hold incoming and outgoing packets
 
 // A UDP instance to let us send and receive packets over UDP
 WiFiUDP Udp;