Bump slugify from 1.6.1 to 1.6.4

Bumps [slugify](https://github.com/simov/slugify) from 1.6.1 to 1.6.4.
- [Release notes](https://github.com/simov/slugify/releases)
- [Commits](https://github.com/simov/slugify/compare/v1.6.1...v1.6.4)

---
updated-dependencies:
- dependency-name: slugify
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

package.json

@@ -59,7 +59,7 @@
     "sass-loader": "^12.3.0",
     "shell-quote": "^1.7.3",
     "shelljs": "0.8.4",
-    "slugify": "^1.6.1",
+    "slugify": "^1.6.4",
     "sortablejs": "^1.14.0",
     "source-code-pro": "^2.38.0",
     "source-map-loader": "^3.0.0",