updating mac canvas role to reflect reality

exposed as role=group in Mac safari and Chrome

Author: stevefaulkner

index.html

@@ -659,13 +659,13 @@ <h3>HTML Element Role Mappings</h3>
                 </td>
                 <td class="ax">
                     <div class="role">
-                        <span class="type">AXRole: </span><code>AXImage</code>
+                        <span class="type">AXRole: </span><code>AXGroup</code>
                     </div>
                     <div class="subrole">
                         <span class="type">AXSubrole: </span><code>(nil)</code>
                     </div>
                     <div class="roledesc">
-                        <span class="type">AXRoleDescription: </span><code>"image"</code>
+                        <span class="type">AXRoleDescription: </span><code>""</code>
                     </div>
                 </td>
                 <td class="comments"></td>