Bump node-sass from 4.12.0 to 4.13.1

Bumps [node-sass](https://github.com/sass/node-sass) from 4.12.0 to 4.13.1.
- [Release notes](https://github.com/sass/node-sass/releases)
- [Changelog](https://github.com/sass/node-sass/blob/master/CHANGELOG.md)
- [Commits](sass/node-sass@v4.12.0...v4.13.1)

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

package.json

@@ -35,7 +35,7 @@
     "breakpoint-sass": "^2.7.1",
     "gulp": "^4.0.2",
     "gulp-file-include": "^2.0.1",
-    "node-sass": "^4.12.0",
+    "node-sass": "^4.13.1",
     "npm-run-all": "^4.1.5",
     "postcss-assets": "^5.0.0",
     "postcss-cli": "^6.1.2",