Fix crasher with xmpp4r.

Under Lita 3.0.1, lita-hipchat crashes on launch because of the new frozen config inside of xmpp4r.

xmpp4r-0.5.6/lib/xmpp4r/jid.rb:40:in `downcase!': can't modify frozen String (RuntimeError)

This dupes the string from the config on connect to prevent the crashing inside of xmpp4r.  All specs passed and now my bot connects again.  I figured instead of complaining I should just send a fix.