This error would arise if Electron version is mismatched - such as using 4.x instead of 7.x (which have incompatible APIs). Seeing that the README still mentions 4.x, I have updated that.
If you were using an AppOnly build, you'll need to download a "regular" build for newer Electron binaries.
If you just downloaded a regular build and this happened, let me know what platform this was on - perhaps I forgot to update the Electron binaries for one of them.