Bump dot-prop from 4.2.0 to 4.2.1 in /ember-electron/backend (#99)

Bumps [dot-prop](https://github.com/sindresorhus/dot-prop) from 4.2.0 to 4.2.1.
- [Release notes](https://github.com/sindresorhus/dot-prop/releases)
- [Commits](sindresorhus/dot-prop@v4.2.0...v4.2.1)

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