Bump node-sass from 4.9.0 to 7.0.0 in /client

Bumps [node-sass](https://github.com/sass/node-sass) from 4.9.0 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/v4.9.0...v7.0.0)

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

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

client/package.json

@@ -42,7 +42,7 @@
     "marked": "^0.3.12",
     "mobx": "^3.4.1",
     "mobx-react": "^4.3.5",
-    "node-sass": "^4.7.2",
+    "node-sass": "^7.0.0",
     "normalize.css": "^7.0.0",
     "nprogress": "^0.2.0",
     "postcss-loader": "^2.0.9",