[css-display] Don't contradict Ruby about non-inline ruby. Fixes #1629.

Author: tabatkins

css-display-3/Overview.bs

@@ -374,11 +374,13 @@ Inner Display Layout Models: the ''flow'', ''flow-root'', ''table'', ''flex'', '
 
 		<dt><dfn>ruby</dfn>
 		<dd>
-			The element generates a principal <a>ruby container</a> box,
+			The element generates a <a>ruby container</a> box
 			and establishes a <a>ruby formatting context</a>
 			in addition to integrating its base-level contents
 			into its parent <a>formatting context</a>
-			if it is inline. [[!CSS3RUBY]]
+			(if it is inline)
+			or generating a wrapper box of the appropriate <a>outer display type</a>
+			(if it is not). [[!CSS3RUBY]]
 	</dl>
 
 	If a <<display-inside>> value is specified but <<display-outside>> is omitted,