rcodezero: fix api documentation url

Author: MikeAT

docs/dns/drivers/rcodezero.rst

@@ -22,7 +22,7 @@ Supported Features:
 - dedicated IP addresses (optional)
 
 Read more at https://www.rcodezero.at/en or get the API documentation
-at https://my.rcodezero.at/api-doc
+at https://my.rcodezero.at/openapi
 
 Instantiating the driver
 ------------------------