Bump node-sass from 4.9.0 to 7.0.0

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](sass/node-sass@v4.9.0...v7.0.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

package.json

@@ -83,7 +83,7 @@
     "flow-webpack-plugin": "1.2.0",
     "html-webpack-plugin": "3.2.0",
     "jest": "24.1.0",
-    "node-sass": "4.13.1",
+    "node-sass": "7.0.0",
     "popper.js": "1.14.3",
     "prop-types": "15.6.2",
     "react": "16.8.0",