res/res_pjsip_pubsub: Fix typo in WARNING message
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Merged revisions 424713 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@424714 f38db490-d61c-443f-a65b-d21fe96a405b