Support Plaster 1.1.0

[daviwil]

Plaster 1.1.0 hasn't been released yet, but anyone who tries to use Plaster from GitHub with the PowerShell extension will see errors like this:

We need to support the changes that have been made to Plaster so that the language server doesn't crash.

Thanks @bgelens!

[rkeithhill]

I haven't done enough testing on PS Core 6 Beta on .NET Core 2 either. I can test on Ubuntu easily enough. Can we configure an AppVeyor build for Ubuntu?

[daviwil]

We have to use Travis CI for Linux and macOS. I had started looking into it in the past but haven't got anything working yet. It'd be good to find a replicable Travis CI setup for all these projects!

[rkeithhill]

Yeah, having cross platform Pester testing would be nice.

[PowerSchill]

The goal would be to add Linux and macOS testing to the Plaster repo or here?

[daviwil]

Both! We'd test PSES here and Plaster at the Plaster repo.

[TylerLeonhardt]

@daviwil looks like we're beyond this issue as Plaster 1.1.3 ships with the vscode extension. Is this about something else?

[daviwil]

Nope, just didn't remember to close it.