Fix modules/zend.json.server.rst broken links

Fix broken links as seen in ```make linkcheck``` output:

>modules/zend.json.server.rst:6: [broken] http://groups.google.com/group/json-rpc/web/json-rpc-1-2-proposal: HTTP Error 404: Not Found
modules/zend.json.server.rst:6: [broken] http://groups.google.com/group/json-schema/web/service-mapping-description-proposal: HTTP Error 404: Not Found
modules/zend.json.server.rst:328: [broken] http://groups.google.com/group/json-schema/web/service-mapping-description-proposal: HTTP Error 404: Not Found