Fix undo

[krassowski]

Fixes https://github.com/jupyterlab-contrib/jupyterlab-vim/issues/89

Builds on top of https://github.com/jupyterlab-contrib/jupyterlab-vim/pull/90 but the changes could be backported standalone.

[github-actions[bot]]

:point_left: Launch a Binder on branch krassowski/jupyterlab-vim/fix-undo

[github-actions[bot]]

:point_left: Launch a binder notebook on branch krassowski/jupyterlab-vim/fix-undo

[ianhi]

@krassowski ok for me to merge #90 first so we can have a nicer git history? As far as I can tell there aren't adidtional changes here correct?

[krassowski]

Yes #90 is ready from my point of view.

[ianhi]

@krassowski I suspect that this will need a rebase