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: Ndependabot[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",

yarn.lock

@@ -7413,10 +7413,10 @@ slide@^1.1.3, slide@^1.1.5, slide@~1.1.3, slide@~1.1.6:
   resolved "https://registry.npmjs.org/slide/-/slide-1.1.6.tgz"
   integrity sha1-VusCfWW00tzmyy4tMsTUr8nh1wc=
 
-slugify@^1.6.1:
-  version "1.6.1"
-  resolved "https://registry.yarnpkg.com/slugify/-/slugify-1.6.1.tgz#a5fcaef29f4e57c6e932ce7044b6ffd9cf81b641"
-  integrity sha512-5ofqMTbetNhxlzjYYLBaZFQd6oiTuSkQlyfPEFIMwgUABlZQ0hbk5xIV9Ydd5jghWeRoO7GkiJliUvTpLOjNRA==
+slugify@^1.6.4:
+  version "1.6.4"
+  resolved "https://registry.yarnpkg.com/slugify/-/slugify-1.6.4.tgz#33d84cc9e859ca3852e6537af6a5ff5bb9e439aa"
+  integrity sha512-Pcz296CK0uGnTf4iNQId79Uv6/5G16t0g0x3OsxWS8qVSOW+JXNnNHKVcuDiMgEGTWyK6zjlWXo2dvzV/FLf9Q==
 
 smart-buffer@^1.0.13:
   version "1.1.15"