Bug#1121228: python-vdf: Switch to fork with key_table argument

[Bastian Germann]

Source: python-vdf
Version: 3.4-5
Severity: normal
Tags: upstream

For updating protontricks to a newer upstream version, the key_table
argument in vdf is needed as described at:
https://github.com/Matoking/protontricks/commit/4198b7ea82369a91e3084d6e185f9b370f78eaec

Please switch to the fork mentioned there:
https://github.com/solsticegamestudios/vdf