Bump node-sass from 4.7.2 to 4.13.1

Bumps [node-sass](https://github.com/sass/node-sass) from 4.7.2 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](https://github.com/sass/node-sass/compare/v4.7.2...v4.13.1)

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

package.json

@@ -29,7 +29,7 @@
 		"babel-cli": "^6.26.0",
 		"babelify": "^8.0.0",
 		"browserify": "^14.5.0",
-		"node-sass": "^4.7.2",
+		"node-sass": "^4.13.1",
 		"node-watch": "^0.5.5"
 	},
 	"dependencies": {