PackageDiff doesn't work from AppVeyor

[ejball]

It throws NuGet.Packaging.Signing.SignatureException.

Unhandled Exception: NuGet.Packaging.Signing.SignatureException
   at NuGet.Packaging.PackageExtractor.VerifyPackageSignatureAsync(String source, Guid parentId, PackageIdentity package, PackageExtractionContext packageExtractionContext, ISignedPackageReader signedPackageReader, CancellationToken token)
   at NuGet.Packaging.PackageExtractor.<>c__DisplayClass3_2.<<InstallFromSourceAsync>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at NuGet.Common.ConcurrencyUtilities.ExecuteWithFileLockedAsync[T](String filePath, Func`2 action, CancellationToken token)
   at NuGet.Packaging.PackageExtractor.InstallFromSourceAsync(String source, PackageIdentity packageIdentity, Func`2 copyToAsync, VersionFolderPathResolver versionFolderPathResolver, PackageExtractionContext packageExtractionContext, CancellationToken token, Guid parentId)
   at NuGet.Protocol.GlobalPackagesFolderUtility.AddPackageAsync(String source, PackageIdentity packageIdentity, Stream packageStream, String globalPackagesFolder, Guid parentId, ILogger logger, CancellationToken token)
   at NuGet.Protocol.GetDownloadResultUtility.<>c__DisplayClass3_0.<<GetDownloadResultAsync>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at NuGet.Protocol.HttpSource.<>c__DisplayClass16_0`1.<<ProcessStreamAsync>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at NuGet.Protocol.HttpSource.ProcessResponseAsync[T](HttpSourceRequest request, Func`2 processAsync, SourceCacheContext cacheContext, ILogger log, CancellationToken token)
   at NuGet.Protocol.HttpSource.ProcessStreamAsync[T](HttpSourceRequest request, Func`2 processAsync, SourceCacheContext cacheContext, ILogger log, CancellationToken token)
   at NuGet.Protocol.GetDownloadResultUtility.GetDownloadResultAsync(HttpSource client, PackageIdentity identity, Uri uri, PackageDownloadContext downloadContext, String globalPackagesFolder, ILogger logger, CancellationToken token)
   at NuGet.Protocol.DownloadResourceV3.GetDownloadResourceResultAsync(PackageIdentity identity, PackageDownloadContext downloadContext, String globalPackagesFolder, ILogger logger, CancellationToken token)
   at Faithlife.PackageDiffTool.LocalPackageHelper.GetPackageAsync(String packageId, NuGetVersion version, Boolean includePrerelease, CancellationToken cancellationToken) in C:\projects\faithlifeapidifftools\src\Faithlife.PackageDiffTool\LocalPackageHelper.cs:line 61
   at Faithlife.PackageDiffTool.MainClass.RunAsync(Options options) in C:\projects\faithlifeapidifftools\src\Faithlife.PackageDiffTool\Program.cs:line 33
   at Faithlife.PackageDiffTool.MainClass.<Main>(String[] args)