MultiUserChat.grantAdmin uses incorrect namespace

Accordingly to the XEP-0045 (http://xmpp.org/extensions/xep-0045.html), in sections "10.6. Granting Admin Status" and "10.7. Revoking Admin Status", the use case of "grant admin status" is done using the "http://jabber.org/protocol/muc#admin" an grant admin status to a mem

However, the MultiUserChat.grantAdmin and MultiUserChat.revokeAdmin methods are using the "muc#owner" namespace.

See the method:

  public void grantAdmin(String jid) throws XMPPErrorException, NoResponseException, NotConnectedException {

        changeAffiliationByOwner(jid, "admin");

    }

It should use the changeAffiliationByAdmin method.