Update nickserv.go

Compare the case-normalized target to Account()

irc/nickserv.go

@@ -1398,7 +1398,7 @@ func nsCertHandler(service *ircService, server *Server, client *Client, command
 	case "add", "del":
 		if 2 <= len(params) {
 			target, certfp = params[0], params[1]
-			if client.Account() == target {
+			if cftarget, err := CasefoldName(target); err == nil && client.Account() == cftarget {
 				// If the target is equal to the account, then the user accidentally invoked operator
 				// syntax (cert add mynick <fp>) instead of self syntax (cert add <fp>).
 				target = ""