Change Subject-C type from UTF8String to PrintableString (#819)

See RFC 5280 page 115: https://tools.ietf.org/html/rfc5280#page-115

Author: emlun

index.bs

@@ -3179,7 +3179,7 @@ The attestation certificate MUST have the following fields/extensions:
 - Version MUST be set to 3 (which is indicated by an ASN.1 INTEGER with value 2).
 - Subject field MUST be set to:
     : Subject-C
-    :: ISO 3166 code specifying the country where the Authenticator vendor is incorporated (UTF8String)
+    :: ISO 3166 code specifying the country where the Authenticator vendor is incorporated (PrintableString)
     : Subject-O
     :: Legal name of the Authenticator vendor (UTF8String)
     : Subject-OU