Add a few missing closing tags

This adds missing </dfn> and </div> tags.

Author: DavMila

web-animations-2/Overview.bs

@@ -2190,7 +2190,7 @@ as follows:
 :   <dfn lt="iteration composite operation replace">replace</dfn>
 ::  Each successive iteration is calculated independently of previous
     iterations.
-:   <dfn lt="iteration composite operation accumulate">accumulate
+:   <dfn lt="iteration composite operation accumulate">accumulate</dfn>
 ::  Successive iterations of the animation are <a
     lt="value accumulation">accumulated</a> with the
     final value of the previous iteration.
@@ -3405,6 +3405,8 @@ partial dictionary KeyframeEffectOptions {
 ::  The <a>iteration composite operation</a> used to define the way
     animation values build from iteration to iteration.
 
+</div>
+
 <h3 id="the-iterationcompositeoperation-enumeration">The IterationCompositeOperation enumeration</h3>
 
 The possible values of an <a>animation effect</a>'s