[css-ruby] Correct figure caption

Author: frivoal

css-ruby-1/Overview.bs

@@ -1432,7 +1432,7 @@ Sharing Annotation Space: the 'ruby-merge' property</h3>
 				          Thus the annotations for “上手”　share space over the second base as in the 'merge' case,
 				          but the annotations for “下手” which are one character each
 				          end up rendering as for 'separate'.">
-				<figcaption>''ruby-merge: separate'' with center alignment</figcaption>
+				<figcaption>''ruby-merge: auto'' with center alignment</figcaption>
 			</figure>
 
 			<div class="note">