Update custom-vnet.md (#1888)

fetching route table assumes user uses json ouptut, which is not always true

docs/custom-vnet.md

@@ -174,11 +174,11 @@ For Kubernetes clusters, we need to update the VNET to attach to the route table
 
 ```
 #!/bin/bash
-rt=$(az network route-table list -g acs-custom-vnet | jq -r '.[].id')
+rt=$(az network route-table list -g acs-custom-vnet -o json | jq -r '.[].id')
 az network vnet subnet update -n KubernetesSubnet -g acs-custom-vnet --vnet-name KubernetesCustomVNET --route-table $rt
 ```
 
 ... where `KubernetesSubnet` is the name of the vnet subnet, and `KubernetesCustomVNET` is the name of the custom VNET itself.
 
 ## Connect to your new cluster
-Once the deployment is completed, you can follow [this documentation](https://docs.microsoft.com/en-us/azure/container-service/container-service-connect) to connect to your new Azure Container Service cluster.
+Once the deployment is completed, you can follow [this documentation](https://docs.microsoft.com/en-us/azure/container-service/container-service-connect) to connect to your new Azure Container Service cluster.