fix: incorrect error message for builtin email pkg introduced by #51

Signed-off-by: Romain Beuque <romain.beuque@corp.ovh.com>

pkg/plugins/builtin/email/email.go

@@ -49,7 +49,7 @@ func validConfig(config interface{}) error {
 	}
 
 	if cfg.SMTPPort == "" {
-		return errors.New("smtp_password is missing")
+		return errors.New("smtp_port is missing")
 	}
 
 	if _, err := strconv.ParseUint(cfg.SMTPPort, 10, 64); err != nil {