Correct placement of TreatNullAs extended attributes

Closes #55.

Author: bathos

index.html

@@ -320,7 +320,7 @@ <h2>Extensibility</h2>
 
   <pre class="idl">
     interface mixin InnerHTML {
-      [CEReactions, TreatNullAs=EmptyString] attribute DOMString innerHTML;
+      [CEReactions] attribute [TreatNullAs=EmptyString] DOMString innerHTML;
     };
 
     Element includes InnerHTML;
@@ -375,7 +375,7 @@ <h2>Extensibility</h2>
 
   <pre class="idl">
     partial interface Element {
-      [CEReactions, TreatNullAs=EmptyString] attribute DOMString outerHTML;
+      [CEReactions] attribute [TreatNullAs=EmptyString] DOMString outerHTML;
       [CEReactions] void insertAdjacentHTML(DOMString position, DOMString text);
     };
   </pre>