Update articles/firewall/premium-migrate.md

Author: ttorble

articles/firewall/premium-migrate.md

@@ -50,7 +50,7 @@ During your migration process, you may need to migrate your Classic firewall rul
 
 1. From the Azure portal, select your standard firewall. On the **Overview** page, select **Migrate to firewall policy**.
 
-   :::image type="content" source="media/premium-migrate/firewall-overview-migrate.png" lightbox="media/premium-migrate/firewall-overview-migrate.png" alt-text="Screenshot showing migrate to firewall policy":::
+   :::image type="content" source="media/premium-migrate/firewall-overview-migrate.png" lightbox="media/premium-migrate/firewall-overview-migrate.png" alt-text="Screenshot showing migrate to firewall policy.":::
 
 1. On the **Migrate to firewall policy** page, select **Review + create**.
 1. Select **Create**.