In his defence, that attribute has been available in browsers since March 2017 according to your link [1], whereas the most recent commit in the repo for the dithering tool was in March 2016 by the looks of it.
https://github.com/gazs/canvas-atkinson-dither
He’s still active on GitHub though, in other repos. Maybe he will accept a pull request? :)
[1]: https://developer.mozilla.org/en-US/docs/Web/API/HTMLAnchorE...