Fix formatting issue

Author: johndowns

articles/reliability/reliability-nat-gateway.md

@@ -188,7 +188,7 @@ The options for testing for zone failures depend on the availability zone config
 
 - *Zone-redundant:* The Azure NAT Gateway platform manages traffic routing, failover, and failback for zone-redundant NAT gateways. Because this feature is fully managed, you don't need to initiate anything or validate availability zone failure processes.
 
-- *Zonal** You're responsible for preparing and testing failover plans in case a zone failure occurs.
+- *Zonal:* You're responsible for preparing and testing failover plans in case a zone failure occurs.
 
 ## Resilience to region-wide failures