fix: [stix2 export] Fixed datetime issue with the 'created' field of some stix objects
fix: [stix2 export] Fixed datetime issue with the 'created' field of some stix objects

- Following some changes on the python stix2
  library, that caused an issue with the previous
  way we created the 'created' field

SteveClement/MISP,SteveClement/MISP,MISP/MISP,SteveClement/MISP,SteveClement/MISP,MISP/MISP,MISP/MISP,MISP/MISP,MISP/MISP,SteveClement/MISP