Upgrade: Bump eslint from 7.20.0 to 7.21.0 (#254)

Bumps [eslint](https://github.com/eslint/eslint) from 7.20.0 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@v7.20.0...v7.21.0)

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

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

package.json

@@ -68,7 +68,7 @@
     "chai": "^4.3.0",
     "deep-equal": "^2.0.5",
     "dockerlint": "^0.3.9",
-    "eslint": "^7.20.0",
+    "eslint": "^7.21.0",
     "jsonlint": "^1.6.3",
     "markdownlint-cli": "^0.26.0",
     "mocha": "^8.3.0",