Bump eslint from 3.19.0 to 4.18.2 in /app

Bumps [eslint](https://github.com/eslint/eslint) from 3.19.0 to 4.18.2.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md)
- [Commits](eslint/eslint@v3.19.0...v4.18.2)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]