Bump node-sass from 4.14.0 to 7.0.0 in /assets

Bumps [node-sass](https://github.com/sass/node-sass) from 4.14.0 to 7.0.0.
- [Release notes](https://github.com/sass/node-sass/releases)
- [Changelog](https://github.com/sass/node-sass/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sass/node-sass/compare/v4.14.0...v7.0.0)

---
updated-dependencies:
- dependency-name: node-sass
  dependency-type: direct:development
...

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

assets/package.json

@@ -21,7 +21,7 @@
     "elm": "^0.19.1-3",
     "elm-webpack-loader": "^6.0.1",
     "mini-css-extract-plugin": "^0.9.0",
-    "node-sass": "^4.13.1",
+    "node-sass": "^7.0.0",
     "optimize-css-assets-webpack-plugin": "^5.0.1",
     "sass-loader": "^8.0.2",
     "terser-webpack-plugin": "^2.3.2",