Editorial: update address element implicit mapping

per the changes to HTML AAM - w3c/html-aam#420
closes #426

Firefox and Chromium browsers have been confirmed to expose address with a group role.  Webkit does not appear to have made this change yet, but someone using macOS with VoiceOver would be none the wiser, since it'll still communicate `<address aria-label=foo>` as a 'group' even though it has not been officially mapped as such.

This is marked as an editorial update as the implicit mapping column is a reflection of reality, and the implicit roles are not defined by this specification.

index.html

@@ -474,7 +474,7 @@ <h2 id="docconformance">
               [^address^]
             </th>
             <td>
-              <a>No corresponding role</a>
+              <code>role=<a href="#index-aria-group">group</a></code>
             </td>
             <td>
               <p>