[css-writing-modes] Show diagram for vertical writing mode (w3c#2762)

This was hidden by mistake in commit fa9120b.

Author: mrego

css-writing-modes-3/Overview.bs

@@ -1583,7 +1583,7 @@ Flow-relative Directions</h3>
   </div>
   <div class="example">
     <figure>
-      <img src="diagrams/sizing-ltr-tb.svg">
+      <img src="diagrams/sizing-ttb-rl.svg">
       <figcaption>Physical/logical terms as applicable to typical Chinese text layout</a>
     </figure>
   </div>

css-writing-modes-4/Overview.bs

@@ -1658,7 +1658,7 @@ Flow-relative Directions</h3>
   </div>
   <div class="example">
     <figure>
-      <img src="diagrams/sizing-ltr-tb.svg">
+      <img src="diagrams/sizing-ttb-rl.svg">
       <figcaption>Physical/logical terms as applicable to typical Chinese text layout</a>
     </figure>
   </div>