Bump node-sass from 4.12.0 to 4.13.0 (#55)

Bumps [node-sass](https://github.com/sass/node-sass) from 4.12.0 to 4.13.0.
- [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/v4.12.0...v4.13.0)

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

package.json

@@ -56,7 +56,7 @@
     "html-webpack-plugin": "^3.2.0",
     "jest": "^24.1.0",
     "mini-css-extract-plugin": "^0.8.0",
-    "node-sass": "^4.11.0",
+    "node-sass": "^4.13.0",
     "prettier": "^1.16.4",
     "sass-loader": "^8.0.0",
     "style-loader": "^1.0.1",