I found a fix!
- Extract the mod.zip into your mods directory.
- Rename the directory 'BlackMarket2-2.0.4' to 'BlackMarket2_2.0.4'.
- In 'path/to/factorio/mods/BlackMarket2_2.0.4/control.lua' change line 8:
from 'require("mod-gui")'
to 'mod_gui = require("mod-gui")'
- Copy the file 'path/to/factorio/data/core/lualib/mod-gui.lua' to 'path/to/factorio/mods/BlackMarket2_2.0.4/'.
- In 'path/to/factorio/mods/BlackMarket2_2.0.4/info.json' on line 9 update the factorio version to '1.1'.
- Have fun!
another edit: Please ignore the following statement.
P.S. You could (and maybe should) skip step 1. and 2. and apply the changes to the zipped mod (or zip it back up afterwards), so when the official update arrives, it's actually updated. (Reason: When an unzipped mod with the same name exists, Factorio will ignore the zipped mod.)