Bump node-sass from 4.9.2 to 4.9.3 in /build

Bumps [node-sass](https://github.com/sass/node-sass) from 4.9.2 to 4.9.3.
- [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/v4.9.2...v4.9.3)

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

build/package.json

@@ -23,7 +23,7 @@
     "karma-junit-reporter": "^1.2.0",
     "karma-phantomjs-launcher": "^1.0.4",
     "karma-viewport": "^1.0.2",
-    "node-sass": "~4.9.0",
+    "node-sass": "~4.9.3",
     "phantomjs-prebuilt": "*",
     "sinon": "<= 5.0.7"
   },