Update contentEditable link to official draft.

Author: whimboo

index.html

@@ -10922,7 +10922,7 @@ <h2>Index</h2>
 
  <dd><p>The HTML Editing APIs specification defines the following terms: [[EDITING]]
   <ul>
-   <!-- Content editable --> <li><dfn><a href=https://w3c.github.io/editing/contentEditable.html>Content editable</a></dfn>
+   <!-- Content editable --> <li><dfn><a href=https://w3c.github.io/contentEditable>Content editable</a></dfn>
    <!-- Editing host --> <li><dfn data-lt="editing hosts"><a href=https://w3c.github.io/editing/execCommand.html#editing-host>Editing host</a></dfn>
   </ul>