chore(deps-dev): bump eslint from 5.16.0 to 6.6.0 in /frontend

Bumps [eslint](https://github.com/eslint/eslint) from 5.16.0 to 6.6.0.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md)
- [Commits](https://github.com/eslint/eslint/compare/v5.16.0...v6.6.0)

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

frontend/package.json

@@ -29,7 +29,7 @@
     "@vue/cli-plugin-eslint": "^4.0.5",
     "@vue/cli-service": "^4.0.5",
     "babel-eslint": "^10.0.3",
-    "eslint": "^5.16.0",
+    "eslint": "^6.6.0",
     "eslint-plugin-vue": "^6.0.0",
     "vue-template-compiler": "^2.6.10"
   },