[web-animations-1] Fix link to KeyframeEffect constructor source argument

Author: birtles

web-animations-1/Overview.bs

@@ -4786,7 +4786,7 @@ interface KeyframeEffect : AnimationEffect {
 
 :   <dfn constructor for=KeyframeEffect lt="KeyframeEffect(source)">KeyframeEffect (source)</dfn>
 ::  Creates a new {{KeyframeEffect}} object with the same properties
-    as {{KeyframeEffect/constructor(source)/source}}
+    as {{KeyframeEffect/KeyframeEffect(source)/source}}
     using the following procedure:
 
     1.  Create a new {{KeyframeEffect}} object, <var>effect</var>.