use one-or-more for dynamic-range-limit-mix grammar production

Author: keithamus

css-color-hdr-1/Overview.bs

@@ -318,7 +318,7 @@ Mixing Dynamic Range Limits: the ''dynamic-range-limit-mix()'' function {#dynami
 
 
 <pre class='prod'>
-	<dfn>dynamic-range-limit-mix()</dfn> = dynamic-range-limit-mix( [ <<ident>> && <<percentage [0,100]>> ]+)
+	<dfn>dynamic-range-limit-mix()</dfn> = dynamic-range-limit-mix( [ <<ident>> && <<percentage [0,100]>> ]#)
 </pre>
 
 <wpt>