acme_tlsa_mail: replace number comparison with else for certificate serials (fixes #5)

acme_tlsa_mail.py

@@ -90,7 +90,7 @@ def check_renewal(cert):
                 LOGGER.debug("Cert for %s matches with the one "
                              "installed, nothing to do.", FQDN)
                 return False
-            elif serial_acme_cert > serial_current_cert:
+            else:
                 return True