Trying to set environment in vs code launch.json on OS X ?

Hi

I'm building an ASP.Net Core RC2 MVC Application on OS X I don't seem to be able to set my environment for development

I think I should be able to add within my launch.json file:

"env": {"ASPNETCORE_ENVIRONMENT": "Development"
}

I've tried adding it within the 

"name": ".NET Core Launch (web)"

"env"

"version": "0.2.0",

Property env is not allowed

Is this an OS X issue? Anyone have any ideas?

Thanks.