Error in webapp module

In the terraform module, [webapp](https://registry.terraform.io/modules/rahulkhengare/webapp/azurerm/0.1.0) referenced from issue
https://github.com/Azure/terraform/issues/16 there seems to be an issue related to the upgrade of terraform 0.11.14 to 0.12.

The following error message is received from the following input in 0.12 and not in 0.11.14

**Error**
```
on .terraform\modules\linuxwebapp\rahulkhengare-terraform-azurerm-webapp-1f4bc69\main.tf line 33,
in resource "azurerm_app_service" "webapp":
33: site_config = "${var.site_config}"

An argument named "site_config" is not expected here. Did you mean to define a
block of type "site_config"?
```

**Input**
```
module "linuxwebapp" {
source = "rahulkhengare/webapp/azurerm"
name = "testmelinuxwebapp"
resource_group_name = "${var.az_rg_name}"
plan_settings = {
kind = "Linux" # Linux or Windows
size = "S2"
capacity = 1
tier = "Standard"

}
}

module "webapp" {
source = "rahulkhengare/webapp/azurerm"
name = "testmewebapp"
resource_group_name = "${var.az_rg_name}"
plan_settings = {
kind = "Windows" # Linux or Windows
size = "S2"
capacity = 1
tier = "Standard"
}
}
```
Found [this ](https://github.com/terraform-providers/terraform-provider-azurerm/commit/9738a21e588a4a220003e12fb2e72ea19f1138fe)and [this](https://github.com/terraform-providers/terraform-provider-azurerm/pull/3210), which seem related but I'm not quite sure.

Start with the referenced webapp module's main.tf at line 33, where site_config is assigned, and compare the Terraform 0.11.14 and 0.12 behavior described in the issue. Review the linked Azure provider commit and pull request, then verify whether the module can be used under Terraform 0.12 without the site_config argument error.

Written by the indexing model from the issue text.