Update interfaces/css-animations.idl (#19429)

Source: https://github.com/tidoust/reffy-reports/blob/ac97ef8/ed/idl/css-animations.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/591867264
diff --git a/interfaces/css-animations.idl b/interfaces/css-animations.idl
index f87015f..9b34bde 100644
--- a/interfaces/css-animations.idl
+++ b/interfaces/css-animations.idl
@@ -3,9 +3,9 @@
 // (https://github.com/tidoust/reffy-reports)
 // Source: CSS Animations Level 1 (https://drafts.csswg.org/css-animations/)
 
-[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;