Minimal example with OCC is displaying empty renderer

This minimal example is displaying nothing for me. OCC works by itself with the JupyterRenderer but I cannot see the OCC shapes created from JupyterCAD.


```
from OCC.Core.BRepPrimAPI import BRepPrimAPI_MakeBox
from jupytercad import CadDocument
doc = CadDocument()
box_shape = BRepPrimAPI_MakeBox(10, 20, 30).Shape()
doc.add_occ_shape(box_shape, name='box')
display(doc)
```