UdpNtpClient example uses old server

[onekopaka]

The NTP server listed in the UdpNtpClient example is going to be shut down in 10 days (December 17th, 2012), according to its' maintainers, NIST. (http://tf.nist.gov/tf-cgi/servers.cgi) This was announced on December 5th, 2012. I'm afraid that people will be confused when the example doesn't work.

Unfortunately, it'd probably be overkill to also have DNS implemented in that file, so I would suggest contuing to use the Boulder area servers. The main NIST servers in Boulder are sometimes busy, but NTP is usually okay. 132.163.4.101-103. Maybe some math in setup() could be used to automatically choose one of these.

[cmaglie]

Fixed the example, thank you.