fix: for half-ipywidgets < 6 compatiblity, VBox is a function, no class
fix: for half-ipywidgets < 6 compatiblity, VBox is a function, no class

maartenbreddels/ipyvolume,maartenbreddels/ipyvolume,maartenbreddels/ipyvolume,maartenbreddels/ipyvolume