Firstly, Democracy 3 has been a great game!
I purchased it from the Mac App Store.
Then, I purchased both Extremism and Social Engineering from the Humble Bundle store.
The extremism update works great. The social engineering DLC had the Lua error, previously discussed in other threads.
I am unable to update Social Engineering to the one that works with the Mac App Store base game, because Steam doesn’t recognise that I have the base Democracy 3 game already installed.
I have emailed Humble Bundle, and after a couple of months (they’re really busy), they finally said that they’ve resolved the problem, and have updated the build on my downloads page.
When I download Social Engineering again, it is still version 1.0, and therefore it hadn’t actually been updated, so I have emailed Humble Bundle again, but as they take ages to reply, I can’t wait any longer and have turned to this forum.
Is there another way I can get an updated version of Social Engineering? Can anybody help? 
Thanks!