Fix modules/zend.feed.pubsubhubbub.rst broken links and table

Fix broken links and table as seen in ```make linkcheck``` output:

>modules/zend.feed.pubsubhubbub.rst:244: [broken] http://www.example.net/rss.xml: HTTP Error 404: Not Found
modules/zend.feed.pubsubhubbub.rst:349: [broken] http://www.example.com/callback?xhub.subscription=key: HTTP Error 404: Not Found
modules/zend.feed.pubsubhubbub.rst:349: [broken] http://www.example.com/callback/key: HTTP Error 404: Not Found
modules/zend.feed.pubsubhubbub.rst:238: [broken] http://www.mydomain.com/hubbub/callback?xhub.subscription=5536df06b5dcb966edab3a4c4d56213c16a8184: HTTP Error 404: Not Found
modules/zend.feed.pubsubhubbub.rst:238: [broken] http://www.mydomain.com/hubbub/callback/5536df06b5dcb966edab3a4c4d56213c16a8184: HTTP Error 404: Not Found