Typo in variable name of pubsub auth request form

in Node.getAuthRequestForm(NodeSubscription), there is a typo in one of the variable names. It is named “pusub#subscriber_jid” instead of “pubsub#subscriber_jid”. It affects (at least) versions 3.6.4 up to current trunk version. Patch (although trivial) is attached.

Thanks, committed to trunk OF-57