Update version of node-xmpp defined in package.json Fixes #121

Fixes the following error: TypeError: Cannot call method 'end' of undefined
Pass xmpp.Element object instead of " " on @jabber.send for ping keepalive

When the arg passed to ping is an empty string a TypeError: Object has no method 'root'
is raised within session.js of the node node-xmpp module. Since the basic premise
of the ping method is to simply perform a keepalive, send through a new xmpp.Element
object instead of an empty string. This object has the root() method that the session
send prototype is looking for.
update dependencies

Signed-off-by: Joshua Rubin <jrubin@zvelo.com>
Merge remote-tracking branch 'crashlytics/stanza-root-fix'