--pre-release is ignored when publishing with --packagePath

[roblourens]

The SSH extension is built and published using a vsix and the --packagePath flag, for example the publish command looks like npx vsce publish --pre-release --packagePath $path --noVerify. Apparently when publishing using that flag, the --pre-release flag is silently ignored and the extension is published as a stable version. Looking over the vsce code, I don't see the problem.

[joaomoreno]

Fixed by #666