Update 6-ldap.md - AUTH_LDAP_USER_DN_TEMPLATE to none for windows 2012+
Update 6-ldap.md - AUTH_LDAP_USER_DN_TEMPLATE to none for windows 2012+

changed     When using Windows Server 2012, `AUTH_LDAP_USER_DN_TEMPLATE` should be set to None.
to Windows Server 2012+
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