On linux, the configuration should sit in ~/.config/aspnet

Many of us are developing .NET Core application on Linux, it is awesome!

It would be even better if Linux standards/conventions were followed. For example, right now, in my home directory, I have a `.aspnet`, `.microsoft` and a `.dotnet` directory.

These should really sit in the [XDG Base Directory](https://wiki.archlinux.org/index.php/XDG_Base_Directory), so they should be in `~/.config/aspnet`, `~/.config/microsoft` and `~/.config/dotnet` respectively, this would avoid further cluttering of the user's home directory.

I did a search before posting this, so apologies if it is a duplicate or if this is the wrong place.