build(deps-dev): bump eslint from 7.19.0 to 7.21.0 in /frontend (#815)

Bumps [eslint](https://github.com/eslint/eslint) from 7.19.0 to 7.21.0.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md)
- [Commits](eslint/eslint@v7.19.0...v7.21.0)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

frontend/package.json

@@ -28,7 +28,7 @@
     "clean-webpack-plugin": "^3.0.0",
     "css-loader": "^5.1.1",
     "css-minimizer-webpack-plugin": "^1.2.0",
-    "eslint": "^7.19.0",
+    "eslint": "^7.21.0",
     "eslint-config-prettier": "^6.2.0",
     "eslint-config-standard": "^16.0.1",
     "eslint-loader": "^4.0.0",