Update dependency postcss-scss to v4 (#460)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

package.json

@@ -31,7 +31,7 @@
     "eslint-config-problems": "^5.0.0",
     "eslint-plugin-prettier": "^3.0.0",
     "postcss": "^8.0.0",
-    "postcss-scss": "^3.0.0",
+    "postcss-scss": "^4.0.0",
     "prettier": "~2.3.0",
     "sugarss": "^4.0.0"
   },