[css-color-5] Add missing 'none' to grammar of device-cmyk, #9445

Author: svgeesus

css-color-5/Overview.bs

@@ -2316,8 +2316,8 @@ or any other color or monochrome output device which has been characterized.
 		The ''device-cmyk()'' function allows authors to specify a color in this way:
 
 		<pre class='prod'>
-			<dfn>device-cmyk()</dfn> = device-cmyk( <<cmyk-component>>{4} [ / <<alpha-value>> ]? )
-			<dfn>&lt;cmyk-component></dfn> = <<number>> | <<percentage>>
+			<dfn>device-cmyk()</dfn> = device-cmyk( <<cmyk-component>>{4} [ / <<alpha-value>> | ''none'' ]? )
+			<dfn>&lt;cmyk-component></dfn> = <<number>> | <<percentage>> | ''none''
 		</pre>
 
 		The arguments of the ''device-cmyk()'' function specify the cyan, magenta, yellow, and black components, in order,