fix prefix in first example

Author: evanp

draft-extensions-policy.html

@@ -71,7 +71,7 @@ <h2>Motivation</h2>
                   "@context": {
                       "ic": "https://flavors.example/ns/icecream#",
                       "favoriteIceCreamFlavor": {
-                          "@id": "pdg:favoriteIceCreamFlavor",
+                          "@id": "ic:favoriteIceCreamFlavor",
                           "@type": "@id"
                       },
                       "Chocolate": "ic:Chocolate",