Update dependency flickity to v3

Author: renovate[bot]

site/package-lock.json

@@ -21,7 +21,7 @@
     "@thulite/images": "^3.3.3",
     "@thulite/seo": "^2.4.2",
     "animejs": "^4.2.2",
-    "flickity": "^2.3.0",
+    "flickity": "^3.0.0",
     "flickity-fade": "^1.0.0",
     "headroom.js": "^0.12.0",
     "scroll-out": "^2.2.12",