[css-ruby-1] Fix markup

Author: fantasai

css-ruby-1/Overview.bs

@@ -1668,7 +1668,7 @@ Changes</h2>
 Changes since the 5 August 2014 WD</h3>
 
 	<ul>
-		<li>Add back 'ruby-overhang: auto | none' for basic control over ruby overhang behavior.
+		<li>Add back ''ruby-overhang: auto | none'' for basic control over ruby overhang behavior.
 		<li>Harmonize inlinification with the <a href="https://www.w3.org/TR/css-display-3/">CSS Display Module</a>.
 		<li>Allow UA to shift ruby/emphasis marks if they conflict with underlines/overlines.
 		<li>Disable auto-hiding when the computed value of 'ruby-merge' is ''collapse''.