Update dependency stylelint-config-standard to v21 (#41)

Co-authored-by: Renovate Bot <[email protected]>

Author: renovate[bot]

package.json

@@ -73,7 +73,7 @@
         "prettier": "^2.0.5",
         "raw-loader": "^4.0.1",
         "stylelint": "^13.6.1",
-        "stylelint-config-standard": "^20.0.0",
+        "stylelint-config-standard": "^21.0.0",
         "stylelint-plugin-stylus": "^0.10.0",
         "ts-node": "^9.0.0",
         "typescript": "^4.0.0",