Upgrading Electron to v39 at least

[RaitoBezarius]

I noticed that the Electron version used in ext/ is v30 in the package.json. v30 has been EOL for the past year and contains probably a bunch of security vulnerabilities inside the web engine.

Could an upgrade to v39 at least be considered?

References: https://endoflife.date/electron

[nadir-ishiguro]

Apart from the security issues, there have been also a bunch of improvements affecting Linux users since then.

I'd really appreciate an update

[paulfitz]

Anyone up for making a PR? The last few upgrades to electron have been pretty easy.