Script should create aspNetCore/environmentVariables XML element

[shinkathe]

Those environmentVariables element should be created if they're missing from aspNetCore element.

I can see that rarely will .net core apps supply with a web.config because of the new configuration system. In these cases IIS will create this file itself, and it will not have environmentVariables element by default, which will cause this script to fail.

Keep up the good work though, this is amazingly useful :)