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>

Author: dependabot[bot]

package-lock.json

@@ -37,7 +37,7 @@
     "cross-env": "^5.0.5",
     "css-loader": "^0.28.7",
     "file-loader": "^1.1.4",
-    "node-sass": "^4.5.3",
+    "node-sass": "^4.13.1",
     "sass-loader": "^6.0.6",
     "vue-loader": "^13.0.5",
     "vue-template-compiler": "^2.4.4",