[css-animations-1] Align with Web IDL specification

Author: autokagami

css-animations-1/Overview.bs

@@ -877,9 +877,9 @@ The <code>AnimationEvent</code> Interface</h3>
 IDL Definition</h4>
 
 	<pre class="idl">
-		[Exposed=Window,
-		 Constructor(CSSOMString type, optional AnimationEventInit animationEventInitDict = {})]
+		[Exposed=Window]
 		interface AnimationEvent : Event {
+		  constructor(CSSOMString type, optional AnimationEventInit animationEventInitDict = {});
 		  readonly attribute CSSOMString animationName;
 		  readonly attribute double elapsedTime;
 		  readonly attribute CSSOMString pseudoElement;