[css-transitions-2] Fix incorrect reference to 'animation' property in note

Author: birtles

css-transitions-2/Overview.bs

@@ -374,7 +374,7 @@ changes to computed values.
 <div class="note">
 As an example, in the following code fragment, when the specified value of
 <code>elem</code>'s 'opacity' property is updated, a user agent may defer
-recalculating the computed value of the 'animation' property.
+recalculating the computed value of the 'opacity' property.
 
 The first time this occurs, calling {{Window/getComputedStyle(elt)}} and
 subsequently accessing the <code>opacity</code> property of the result will