Add level to canonical URL of css-color-hdr (#1542)

The draft used to be without a level but gained one recently, changing the
actual shortname of the spec:
w3c/csswg-drafts@2329ab2

(Build failed because it could no longer find the path to the source in the
GitHub repository)

specs.json

@@ -93,7 +93,12 @@
   },
   "https://drafts.csswg.org/css-borders-4/",
   "https://drafts.csswg.org/css-color-6/ delta",
-  "https://drafts.csswg.org/css-color-hdr/",
+  {
+    "url": "https://drafts.csswg.org/css-color-hdr-1/",
+    "formerNames": [
+      "css-color-hdr"
+    ]
+  },
   "https://drafts.csswg.org/css-conditional-values-1/",
   "https://drafts.csswg.org/css-display-4/",
   "https://drafts.csswg.org/css-env-1/",