diagrams not rendered on site

[VladimirAlexiev]

https://www.relaton.org/specs/relaton-model-diagrams/ doesn't actually show the diagrams.
Eg https://www.relaton.org/specs/relaton-model-diagrams/RelBib_Collection/ shows a broken image.

[opoudjis]

The broken image is

<img class="leaflet-image-layer leaflet-zoom-animated" src="/specs/relaton-model-diagrams/images/RelBib_Collection.png" alt style="z-index: 1; transform: translate3d(175px, 58px, 0px); width: 400px; height: 284px;">

That directory is populated from https://github.com/relaton/relaton-models as a git submodule, and the image is there:

So someone more conversant with Jekyll than me is going to need to work out what has happened here. Assigning to @strogonoff and @ronaldtse