Switch mac build to universal build

Apple's documentation suggests that apps should be shipped as universal binaries
to simplify the process for the users. See eg. https://developer.apple.com/documentation/apple-silicon/porting-your-macos-apps-to-apple-silicon



Also update electron-updater to latest version (matching electron-builder version)
as part of this.

Signed-off-by: Christoph Settgast <csett86@web.de>