Upgrade preact to v10.20.0

The upstream preact bug [1] has been fixed now!

[1]: https://github.com/preactjs/preact/issues/4221

package.json

@@ -4,7 +4,7 @@
   "dependencies": {
     "htm": "^3.0.4",
     "linkifyjs": "^4.1.3",
-    "preact": "10.17.1"
+    "preact": "^10.20.0"
   },
   "devDependencies": {
     "@parcel/packager-raw-url": "^2.0.0",