Plaster v2.0.0-alpha broken on Windows

[gaelcolas]

Hiya,

Sampler uses Plaster and we've noticed on our pipelines that the prerelease version breaks on windows because Write-PlasterLog uses the Null-coalescing operator.

https://github.com/PowerShellOrg/Plaster/blob/v2/Plaster/Private/Write-PlasterLog.ps1#L52-L54

Could you please fix soonish, or would you recommend we pin an old version?