Change definition of space-like to tream semantics/maction as mrow

See w3c/mathml#160

Author: fred-wang

index.html

@@ -1858,14 +1858,11 @@ <h3>Definition of space-like elements</h3>
                 <a>unknown MathML element</a>,
                 <a><code>&lt;mrow&gt;</code></a>,
                 <a><code>&lt;mstyle&gt;</code></a>,
-                <a><code>&lt;mphantom&gt;</code></a> or
-                <a><code>&lt;mpadded&gt;</code></a>
-                all of whose in-flow children are <a>space-like</a>;
-              </li>
-              <li>
-                An <a><code>&lt;maction&gt;</code></a>
-                or <a><code>&lt;semantics&gt;</code></a> element
-                whose first in-flow child exists and is <a>space-like</a>.
+                <a><code>&lt;mphantom&gt;</code></a>,
+                <a><code>&lt;mpadded&gt;</code></a>,
+                <a><code>&lt;maction&gt;</code></a>
+                or <a><code>&lt;semantics&gt;</code></a>
+                all of whose in-flow children are <a>space-like</a>.
               </li>
             </ul>
             <div class="note">