Fully qualify URL for example social media service.

Co-authored-by: Dave Longley <[email protected]>

Author: msporny

index.html

@@ -1197,7 +1197,7 @@ <h2>Services</h2>
       "publicKeyMultibase": "z6MkmM42vxfqZQsv4ehtTjFFxQ4sQKS2w6WR7emozFAn5cxu"
   }],
   <span class="highlight">"service": [{
-    "type": "ExampleSocialMediaService",
+    "type": "https://social.example/ExampleSocialMediaService",
     "serviceEndpoint": "https://warbler.example/sal674"
   }]</span>
 }