[web-animations-1] Add missing closing div tag

Author: birtles

web-animations-1/Overview.bs

@@ -5760,6 +5760,8 @@ The {{KeyframeEffect}} interface {#the-keyframeeffect-interface}
       Examples of the usage of this constructor are given in
       [[#creating-a-new-keyframeeffect-object]].
 
+      </div>
+
   : <dfn lt="KeyframeEffect(source)">KeyframeEffect (source)</dfn>
   ::
       Creates a new {{KeyframeEffect}} object