[css-color-4][editorial] use the right syntax, sigh

Author: svgeesus

css-color-4/Overview.bs

@@ -968,7 +968,7 @@ Representing Colors: the <<color>> type</h2>
 <h4 id="color-syntax-modern">
 Modern (Space-separated) Color Function Syntax</h4>
 
-	All of the <<absolute-color>> functional forms
+	All of the [=absolute color=] functional forms
 	first defined in this specification
 	use the <dfn export>modern color syntax</dfn>,
 	meaning: