Get-RequestRow fails to convert date when regional settings are not en-US

[Get-RequestRow](https://github.com/Crypt32/PSPKI/blob/master/PSPKI/Server/Get-RequestRow.ps1#L76) fails to convert date with current code, when user regional settings are something other than English (US).

When changing `[cultureinfo]` reference to `[Globalization.CultureInfo]::CurrentCulture`, the code would work with any regional setting.