Update node-sass requirement to ~4.9.0 in /build

Updates the requirements on [node-sass](https://github.com/sass/node-sass) to permit the latest version.
- [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/commits/v4.9.0

)

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

build/package.json

@@ -24,7 +24,7 @@
     "karma-phantomjs-launcher": "*",
     "karma-viewport": "^0.4.2",
     "phantomjs-prebuilt": "*",
-    "node-sass": "~4.1.1",
+    "node-sass": "~4.9.0",
     "sinon": "<= 5.0.7"
   },
   "engine": "node >= 6.9"