Update alternate xml link tag to be W3 compliant
Update alternate xml link tag to be W3 compliant

The link tag being produced was not W3 compliant as it was using the nofollow value in the rel attribute on a link tag which is not permitted as per the W3 standards http://www.w3.org/TR/html5/links.html#linkTypes
mandrew/silverstripe-versionfeed,silverstripe-labs/silverstripe-versionfeed