electron-prebuilt deprecated

[jmhibben]

While building Abricotine from source, npm issued the following warning:

npm WARN deprecated electron-prebuilt@1.3.9: electron-prebuilt has been renamed to electron. For more details, see http://electron.atom.io/blog/2016/08/16/npm-install-electron

This should be corrected in package.json before the electron-prebuilt package is too far outdated or removed.

[darahak]

Note: electron-prebuilt will stop being updated after the end of this year.