Proxifier CI is borked

[Nathaniel J. Smith]

FYI, proxifier just released a new version, and apparently it doesn't use an LSP anymore?

Quick fix: python-trio/trio#1780

[Bert Belder]

@njsmith Thanks for the heads up! After clearing the AppVeyor cache I this my CI went red as well.

I opted to put the LSP installers in a gist and download them from there: 183993f.