fix(app): disable app downgrade feature
fix(app): disable app downgrade feature

Ensure that we set electron-updater `allowDowngrade=false` after
setting the update channel, since `autoUpdater.channel` is a setter
which explicity sets `allowDowngrade=true`.

LN-Zap/zap-desktop,LN-Zap/zap-desktop,LN-Zap/zap-desktop