The site https://pluto-on-binder.glitch.me/ was still using an old version of Julia and Pluto. I just updated, try again!
The example notebook uses Pkg to set up a package environment, because it was written before 馃巵 Package management 路 fonsp/Pluto.jl Wiki 路 GitHub existed! You should definitely use the built-in package manager for binder, which will also fix this issue.