build(deps-dev): bump eslint from 7.19.0 to 7.21.0

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-preview[bot] <support@dependabot.com>

package.json

@@ -25,7 +25,7 @@
     "cartesian": "^1.0.1",
     "clean-webpack-plugin": "^3.0.0",
     "coveralls": "^3.1.0",
-    "eslint": "^7.19.0",
+    "eslint": "^7.21.0",
     "get-permutations": "^1.0.0",
     "html-webpack-plugin": "^4.5.1",
     "jest": "^26.6.3",