Bump node-sass from 4.12.0 to 4.13.1 in /examples/complex

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]

examples/complex/package-lock.json

@@ -33,7 +33,7 @@
         "file-loader": "^3.0.1",
         "html-webpack-plugin": "^3.2.0",
         "mini-css-extract-plugin": "^0.5.0",
-        "node-sass": "^4.11.0",
+        "node-sass": "^4.13.1",
         "resolve-url-loader": "^3.0.1",
         "sass-loader": "^7.1.0",
         "style-loader": "^0.23.1",