Narrative.div shall have xhtml namespace

[yunwwang]

FHIR standard specifies that Narrative.div is type of xhtml (http://build.fhir.org/narrative.html#xhtml). It shall have namespace like:
<div xmlns="http://www.w3.org/1999/xhtml">
Current cruicible does not generate this namespace which causes validation failure when testing .validate from some FHIR server such as HAPI
Here is the narrative generated from cruicible:

  "text": {
       "status": "generated",
       "div": "<div>vdMWxFkc4xRhWv8XQHWUBg==</div>"
  },

The error message while posting to Patient/$validate endpoint on HAPI server is:

processing: Wrong namespace on the XHTML ('null')