Bump OmniSharp to v0.19.2

[andyleejordan]

Update v0.19.1 contains a critical bugfix, OmniSharp/csharp-language-server-protocol#562, necessary for us to complete PowerShell/vscode-powershell#3294.

[rjmholt]

Unfortunately the latest Omnisharp update currently breaks integration with VSCode's debugging UI:

[rjmholt]

Waiting on OmniSharp/csharp-language-server-protocol#567 to fix this

[andyleejordan]

Thanks for your diligent work @rjmholt!

[andyleejordan]

I think we should also wait for OmniSharp/csharp-language-server-protocol#556 and hopefully once it's resolved a v0.19.2 drop.

[andyleejordan]

This was resolved by #1460 (which is a beta of 0.19.2, but for now it counts). When a stable version is released, we'll update again.