0.18.13

This is 0.18.13-beta4 with one change: it downloads elm-interface-to-json from the below release assets rather than from Bintray which was sunset 2021-05-01.

This allows people who still are on Elm 0.18 to run their tests (use npm install elm@latest-0.18.0 to install Elm 0.18 itself – requires Node.js 10).