Fix unref error

[mifi]

See #399

[ehmicky]

Thanks a lot for this PR @mifi! 🎉

This looks good to me (except for one small detail)!

[ehmicky]

Waiting for @sindresorhus to review it as well.

[sindresorhus]

Would be good to open an issue on Electron about this and add a code comment that links to that issue.

[ehmicky]

@sindresorhus Would it be ready to merge otherwise?

[sindresorhus]

Yes, I just like to give context to workarounds and ensure it will be fixed upstream eventually.

[mifi]

I found these:

• Uncaught TypeError: setInterval(...).unref is not a function in node enabled renderer or web worker electron/electron#21162
• setInterval().unref() is not a function electron/electron#12462

[sindresorhus]

@ehmicky This still needs a code comment about why it's guarded. For example:

Guarded because there's no .unref when execa is used in the renderer process in Electron.

[ehmicky]

Oops, I thought this was ok to merge, sorry about that.
I've added the comment in #401.

[thislooksfun]

Is it possible to backport this fix to 3.x.x? (ref: nklayman/vue-cli-plugin-electron-builder#647 (comment))