Editorial: use new constructor syntax from WebIDL (#296)

Author: Marcos Cáceres

index.bs

@@ -2098,9 +2098,9 @@ attribute is the event handler for the
 This specification fires events with the following custom interfaces:
 
 <xmp class=idl>
-[Exposed=(Window,Worker),
- Constructor(DOMString type, optional IDBVersionChangeEventInit eventInitDict = {})]
+[Exposed=(Window,Worker)]
 interface IDBVersionChangeEvent : Event {
+  constructor(DOMString type, optional IDBVersionChangeEventInit eventInitDict = {});
   readonly attribute unsigned long long oldVersion;
   readonly attribute unsigned long long? newVersion;
 };