I eventually got to fix it (thanks arctic)! The
minimap v2.0.1 now officially works for 2.8.0 . And while I was here I also implemented
sliders. I hope you won't mind.

So now instead of having to type numbers, you can slide it and it zooms more or less. Hopefully it should make the zooming feature more interesting, but it might break your previous settings.

Very small zoom (< 1)

Very big zoom (> 5)

Okay zoom (~1.75)
You don't need to download anything other than
the attached minimap_v2.zip . As usual,
unzip it in your Plugins folder.
You should end up with this:
Plugins\minimap_v2.gml
Plugins\minimap\(5 .gml files)
Plugins\Resources\YB\slider\(2 .png and 1 .gml)