[css-images-3] remove && from <linear-color-stop> syntax (w3c#8021)

Author: 12Me21

css-images-3/Overview.bs

@@ -899,7 +899,7 @@ Color Stop Lists</h4>
 	<pre class=prod>
 		<dfn>&lt;color-stop-list></dfn> =
 			<<linear-color-stop>> , [ <<linear-color-hint>>? , <<linear-color-stop>> ]#
-		<dfn>&lt;linear-color-stop></dfn> = <<color>> && <<length-percentage>>?
+		<dfn>&lt;linear-color-stop></dfn> = <<color>> <<length-percentage>>?
 		<dfn>&lt;linear-color-hint></dfn> = <<length-percentage>>
 	</pre>