[css-grid-2] Switch <positive-integer> to <integer [1, Infinity]>

Author: tabatkins

css-grid-2/Overview.bs

@@ -136,7 +136,7 @@ Establishing a Subgrid</h3>
 	<pre class="prod">
 		<dfn>&lt;line-name-list></dfn> = [ <<line-names>> | <<name-repeat>> ]+
 		<dfn>&lt;line-names></dfn>     = '[' <<custom-ident>>* ']'
-		<dfn>&lt;name-repeat></dfn>    = repeat( [ <<positive-integer>> | auto-fill ], <<line-names>>+)
+		<dfn>&lt;name-repeat></dfn>    = repeat( [ <<integer [1, Infinity]>> | auto-fill ], <<line-names>>+)
 	</pre>
 
 	The <<name-repeat>> variant of the ''repeat()'' notation