Error when using "deploy to Azure" from quickstarts page. The template doesn't validate.

[Three VM Sharepoint Deployment](https://azure.microsoft.com/en-us/resources/templates/sharepoint-three-vm/)

### Issue Details
{
"telemetryId": "d41b85fb-e538-4211-9b73-3093c23722b0",
"bladeInstanceId": "Blade_0fae8553579049e8b9811d2f7d96ee7f_0_0",
"galleryItemId": "Microsoft.Template",
"createBlade": "DeployToAzure",
"code": "InvalidTemplate",
"message": "Deployment template validation failed: 'The template resource 'spfarm-ad/InstallDomainController' for type 'extensions' at line '97' and column '9' has incorrect segment lengths. A nested resource type must have identical number of segments as its resource name. A root resource type must have segment length one greater than its resource name. Please see https://aka.ms/arm-template/#resources for usage details.'."
}

### Repro steps
1. Go to https://azure.microsoft.com/en-us/resources/templates/sharepoint-three-vm/
2. Click "deploy to Azure"
3. Add parameter values where necessary.
4. click "Purchase"
5. Get validation error.

Start at the Three VM SharePoint Deployment template linked in the issue and reproduce the failure through its “deploy to Azure” flow. Inspect the resource reported at line 97, then validate the template with the supplied parameters; done means deployment-template validation succeeds without the incorrect segment-length error.

Written by the indexing model from the issue text.