[css-color-5] add xyz adjuster to grammar

Author: svgeesus

css-color-5/Overview.bs

@@ -97,7 +97,7 @@ Mixing colors: the ''color-mix'' function {#colormix}
 </pre>
 
 <pre class='prod'>
-	<dfn>color-adjuster</dfn> = <<rgb-adjuster>> | <<hsl-adjuster>> | <<hwb-adjuster>> | <<lab-adjuster>> | <<lch-adjuster>>
+	<dfn>color-adjuster</dfn> = <<rgb-adjuster>> | <<hsl-adjuster>> | <<hwb-adjuster>> | <<xyz-adjuster>> | <<lab-adjuster>> | <<lch-adjuster>>
 	<dfn>srgb-adjuster</dfn> = red | green | blue
 	<dfn>hsl-adjuster</dfn> = <<hue-adjuster>> | saturation | lightness
 	<dfn>hwb-adjuster</dfn> = <<hue-adjuster>> |  whiteness | blackness