Move to PowerShellStandard or rev the versions of the PowerShell SDK

[TylerLeonhardt]

The version here is pretty outdated:

https://github.com/Jaykul/Jupyter-PowerShell/blob/master/Source/PowerShell-Kernel/PowerShell-Kernel.csproj#L54

6.0 isn't in support anymore.

I'd be cool to have the versions updated so folks can use the latest version with Azure Data Studio's Notebooks:

https://github.com/microsoft/azuredatastudio/issues/4593