Bump electron from 39.0.0 to 39.8.4

Bumps [electron](https://github.com/electron/electron) from 39.0.0 to 39.8.4.
- [Release notes](https://github.com/electron/electron/releases)
- [Commits](https://github.com/electron/electron/compare/v39.0.0...v39.8.4)

---
updated-dependencies:
- dependency-name: electron
  dependency-version: 39.8.4
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>