[css-grid-3] Make masonry-slack animatable w3c#9328

Author: tabatkins

css-grid-3/Overview.bs

@@ -1018,7 +1018,7 @@ Placement Precision: the 'masonry-slack' property</h3>
 	Inherited: no
 	Applies to: [=masonry containers=]
 	Computed value: a computed length
-	Animation type: discrete
+	Animation type: as length
 	</pre>
 
 	[=Masonry containers=] are filled