Bump node-sass from 4.14.1 to 7.0.0 in /app

Bumps [node-sass](https://github.com/sass/node-sass) from 4.14.1 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/v4.14.1...v7.0.0)

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

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

app/package.json

@@ -132,7 +132,7 @@
     "lint-staged": "9.5.0",
     "mini-css-extract-plugin": "0.9.0",
     "mobx": "^5.15.1",
-    "node-sass": "^4.14.1",
+    "node-sass": "^7.0.0",
     "npm-check-updates": "4.0.1",
     "optimize-css-assets-webpack-plugin": "5.0.3",
     "prettier": "1.19.1",