Winepack cannot be enabled due to outdated cert

When following instructions from website:

```
➤ flatpak remote-add --if-not-exists winepak https://dl.winepak.org/repo/winepak.flatpakrepo
error: Signature made vie 20 jul 2018 03:30:34 using RSA key ID A959831C080B608F
BAD signature from " <julian@richen.io>"
Key expired mar 09 jun 2020 19:16:34
```