Bump sortablejs from 1.14.0 to 1.15.0

Bumps [sortablejs](https://github.com/SortableJS/Sortable) from 1.14.0 to 1.15.0.
- [Release notes](https://github.com/SortableJS/Sortable/releases)
- [Commits](https://github.com/SortableJS/Sortable/compare/1.14.0...1.15.0)

---
updated-dependencies:
- dependency-name: sortablejs
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

package.json

@@ -68,7 +68,7 @@
     "shell-quote": "^1.7.3",
     "shelljs": "0.8.5",
     "slugify": "^1.6.5",
-    "sortablejs": "^1.14.0",
+    "sortablejs": "^1.15.0",
     "source-code-pro": "^2.38.0",
     "source-map-loader": "^3.0.1",
     "source-sans-pro": "3.6.0",