Update dependency node-sass to v6

Author: renovate-bot

frontend/package-lock.json

@@ -41,7 +41,7 @@
     "eslint": "6.8.0",
     "eslint-plugin-vue": "7.9.0",
     "geckodriver": "1.22.3",
-    "node-sass": "5.0.0",
+    "node-sass": "6.0.0",
     "sass-loader": "10.2.0",
     "typescript": "4.2.4",
     "vue-jest": "5.0.0-alpha.9"