Bump gem versions

Bring gem dependencies up to date. Use latest Lita v3.0

There's a notice in README that `lita-hipchat` can be used instead for generic xmpp chats, but it's actually not true since `lita-hipchat` adapter has some hipchat-specific configurations and doesn't work with other xmpp chats.

I got this plugin working with latest Lita by fixing a couple issues.