Keep sync-exclude.lst when uninstalling during update

Please don’t overwrite the sync-exclude.lst file when performing an automatic uninstall of the current version in the course of an client update.

I just had to manually delete a lot of files since the file has been overwritten and stuff has been uploaded/downloaded to and from clients erroneously since i wasn’t aware of this until now. Also I’m pretty sure that I’m going to “trap” into this again during future updates…

Please report this to the bugtracker https://github.com/nextcloud/client_theming/issues

Don’t forget to provide more information, e.g. between which versions you run the update.