Bump electron from 1.4.12 to 2.0.18

Bumps [electron](https://github.com/electron/electron) from 1.4.12 to 2.0.18.
- [Release notes](https://github.com/electron/electron/releases)
- [Changelog](https://github.com/electron/electron/blob/master/docs/breaking-changes.md)
- [Commits](electron/electron@v1.4.12...v2.0.18)

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Author: dependabot[bot]