Ping Pong example update

The Ping Pong example does not work by just changing the credentials for both accounts.

After some investigation I realized that JID objects are compared using `==` and `eql()` by using node, domain and resource. Because of this, a newly instanciated JID (which does not have resource) will not be equal to a JID coming from a presence/status stanza.

This updated example works for me.

Please let me know if I can/should change anything.