[css-overflow-3] Make block-end padding inside block container scroll containers required, matching implementations. w3c#129

Author: fantasai

css-overflow-3/Overview.bs

@@ -281,11 +281,10 @@ Scrollable Overflow</h3>
 			is increasing the size of the [=scrollable overflow rectangle=].
 
 			Including this padding is optional for <a>block containers</a>
-			in any axis whose corresponding <a>content-distribution property</a>
-			('align-content'/'justify-content')
-			is ''align-content/normal''.
+			in the inline axis if 'align-content'
+			is ''justify-content/normal''.
 
-			Issue(129): It's not yet clear if including the padding here is Web-compatible,
+			Issue(129): It's not yet clear if including inline-axis padding here is Web-compatible,
 			so this clause is optional while under investigation.
 			Existing behavior in the inline axis is
 			<a href="http://jsbin.com/digadoyohi/1/edit?html,css,output">not</a>