Fix the repo build for Apple M1 laptops

[trekhleb]

See the Can't install canvas npm package on Apple M1 issue for more details.

Basically, the solution is to replace the node-canvas with pngjs npm package.

Keeping the node-canvas package would require the M1 users to install the following dependencies (which is the overhead for this repo): brew install pkg-config cairo pango libpng jpeg giflib librsvg