Ipywidgets fix

Addition to the fix !17 (merged). It appeared as the problem is with nglview. However the problem was with the library that gets installed along nglview -> ipywidgets. The latest update messed up connection with nglview. Downgrading to version <8 fixes the issue.

Reposting original issue that describes the problem: https://github.com/nglviewer/nglview/issues/1032