Fix one inconsistent use of [] in examples. (#759)

Author: jan-ivar

index.bs

@@ -13390,11 +13390,9 @@ The {{DOMException}} type is an [=interface type=] defined by the following IDL
 fragment:
 
 <pre class="idl">
-[
- Exposed=(Window,Worker),
+[Exposed=(Window,Worker),
  Constructor(optional DOMString message = "", optional DOMString name = "Error"),
- Serializable
-]
+ Serializable]
 interface DOMException { // but see below note about ECMAScript binding
   readonly attribute DOMString name;
   readonly attribute DOMString message;