Update dependency critters to v0.0.21

Author: renovate[bot]

site/package.json

@@ -28,7 +28,7 @@
     "@types/node": "16.6.2",
     "@types/react": "17.0.19",
     "autoprefixer": "10.3.3",
-    "critters": "0.0.10",
+    "critters": "0.0.21",
     "dotenv": "10.0.0",
     "gray-matter": "4.0.3",
     "next-mdx-remote": "3.0.4",