[css-multicol-1] Make bikeshed happy

Author: frivoal

css-multicol/Overview.bs

@@ -842,7 +842,7 @@ Column gaps and rules</h2>
 	Inherited: no
 	Percentages: N/A
 	Media: visual
-	Computed value: absolute length; ''0'' if the column rule style is ''none'' or ''hidden''
+	Computed value: absolute length; ''0'' if the column rule style is ''border-style/none'' or ''hidden''
 	Animatable: as <<length>>
 	</pre>