Fixes #4459 "issuserAltName" documentation typo.

See crypto/objects/objects.txt:767 -- field is "issuerAltName"
CLA: trivial
Reviewed-by: NAndy Polyakov <appro@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4460)

doc/man5/x509v3_config.pod

@@ -205,7 +205,7 @@ certificate (if possible).
 
 Example:
 
- issuserAltName = issuer:copy
+ issuerAltName = issuer:copy
 
 
 =head2 Authority Info Access.