Remy Sharp has published a post all about how to cross-post to medium, you can read it over here.
The crux of the issue was that Medium had remove their IFTTT applet and therefore there was no longer a straight foward way to do this (although the meat and potatoes of the article is how to do it yourself).
Fortunately, if you’re running WordPress, you can quite easily cross post to Medium using the Medium Plugin. Although it isn’t being supported at the moment (from what I can see), I’m using it at the moment and if you’re reading this on Medium then it works.