[css-color] Fix spacing

Author: frivoal

css-color/Overview.bs

@@ -184,7 +184,7 @@ Resolving Color values</h2>
 		so descendants will use their own 'color' property to resolve it.
 
 		<li>
-		The computed value and used value of ''<color>/transparent'' is ''rgba(0,0,0,0)''.
+		The computed value and used value of ''<color>/transparent'' is ''rgba(0, 0, 0, 0)''.
 
 		Issue: Gecko disagrees, and serializes any <<color>> with an alpha channel of 0 as transparent.
 		No other browser does that though.