[OAIRecord] Fix setSpec order in header
openarchive.org validates a OAI repository even if the order of the elements in the header is not respected. However, the OAI-PMH xsd states that setSpec should be placed after identifier and datestamp.
openarchive.org validates a OAI repository even if the order of the elements in the header is not respected. However, the OAI-PMH xsd states that setSpec should be placed after identifier and datestamp.