Update for new ipycanvas

[matthewturk]

We need to make sure we're up to date for https://github.com/martinRenou/ipycanvas/pull/111 where the way the layout and image sizes are affected once #53 goes in.

[martinRenou]

Note that the default behavior of ipycanvas should not change. You might see ipycanvas behavior changes only if you manipulate the layout property.

[matthewturk]

@martinRenou Thanks! What I want to check is that we're also getting our image size correct, since we supply that in the browser to a callback to generate the data. It's entirely possible we're doing everything as we should, but I just wanted to make a note in case we weren't. 😁