change 2 instances of should not to not recommended (#532)

see #530

Author: scottaohara

index.html

@@ -594,7 +594,7 @@ <h2 id="docconformance">
             </td>
             <td>
               <p>
-                <a><strong>Any `role`</strong></a>, though <a href="#index-aria-group">`group`</a> SHOULD NOT be used.
+                <a><strong>Any `role`</strong></a>, though <a href="#index-aria-group">`group`</a> is NOT RECOMMENDED.
               </p>
               <p>
                 Otherwise, <a data-cite="wai-aria-1.2#global_states">global `aria-*` attributes</a> 
@@ -1481,7 +1481,7 @@ <h2 id="docconformance">
             </td>
             <td>
               <p>
-                <a><strong>Any `role`</strong></a>, though <a href="#index-aria-group">`group`</a> SHOULD NOT be used.
+                <a><strong>Any `role`</strong></a>, though <a href="#index-aria-group">`group`</a> is NOT RECOMMENDED.
               </p>
               <p>
                 Otherwise, <a data-cite="wai-aria-1.2#global_states">global `aria-*` attributes</a>