[css-ruby] Fix figure caption

Author: frivoal

css-ruby-1/Overview.bs

@@ -1401,7 +1401,7 @@ Sharing Annotation Space: the 'ruby-merge' property</h3>
 				          In the case of “上手”, the “う” from the first base’s annotation
 				          and the “ず” from the second base’s annotation end up
 				          sharing space over the second base.">
-				<figcaption>''ruby-merge: separate'' with center alignment</figcaption>
+				<figcaption>''ruby-merge: merge'' with center alignment</figcaption>
 			</figure>
 
 			<div class="example">