FIX: Resolve short URLs after diffHTML was loaded (#14296)

Short URLs were resolved before diffHTML was loaded and content was
swapped by it, which meant that no URLs were found and the URLs remained
unsolved. This caused image elements to be blank.

* DEV: Updated diffHTML to 1.0.0-beta.20

package.json

@@ -6,6 +6,7 @@
   "author": "Discourse",
   "license": "GPL-2.0-only",
   "dependencies": {
+    "@discourse/itsatrap": "^2.0.10",
     "@fortawesome/fontawesome-free": "5.11.2",
     "@highlightjs/cdn-assets": "^10.6.0",
     "@json-editor/json-editor": "^2.5.2",
@@ -21,7 +22,7 @@
     "bootstrap": "v3.4.1",
     "chart.js": "3.5.1",
     "chartjs-plugin-datalabels": "^2.0.0",
-    "diffhtml": "^1.0.0-beta.18",
+    "diffhtml": "^1.0.0-beta.20",
     "eslint-config-discourse": "^1.1.8",
     "handlebars": "^4.7.7",
     "jquery": "3.5.1",
@@ -41,8 +42,7 @@
     "workbox-expiration": "^4.3.1",
     "workbox-routing": "^4.3.1",
     "workbox-strategies": "^4.3.1",
-    "workbox-sw": "^4.3.1",
-    "@discourse/itsatrap": "^2.0.10"
+    "workbox-sw": "^4.3.1"
   },
   "devDependencies": {
     "@arkweid/lefthook": "^0.7.2",