Update Azure PowerShell cmdlet

Existing example still mentioned AzureRm PowerShell module (Get-AzureRmContext). Update to new Az PowerShell module cmdlet

Author: luisarnauth

articles/azure-netapp-files/develop-rest-api-powershell.md

@@ -79,7 +79,7 @@ The REST API specification for Azure NetApp Files is published through [GitHub](
 5. Send a test call and include the token to validate your access to the REST API:
 
     ```azurepowershell
-    $SubId = (Get-AzureRmContext).Subscription.Id 
+    $SubId = (Get-AzContext).Subscription.Id 
     Invoke-RestMethod -Method Get -Headers $headers -Uri https://management.azure.com/subscriptions/$SubId/providers/Microsoft.Web/sites?api-version=2019-11-01
     ```
 
@@ -432,4 +432,4 @@ This section shows sample scripts for PowerShell.
 
 ## Next steps
 
-[See the Azure NetApp Files REST API reference](/rest/api/netapp/)
+[See the Azure NetApp Files REST API reference](/rest/api/netapp/)