[css-grid] Fix grammar error in <link-name-list>

Author: fantasai

css-grid/Overview.src.html

@@ -777,7 +777,7 @@ <h3 id='track-sizing'>
 		<dfn>&lt;track-size></dfn>     = minmax( <<track-breadth>> , <<track-breadth>> ) | auto | <<track-breadth>>
 		<dfn>&lt;track-breadth></dfn>  = <<length>> | <<percentage>> | <<flex>> | min-content | max-content
 		<dfn>&lt;line-names></dfn>     = ( <<ident>>* )
-		<dfn>&lt;line-name-list></dfn> = [ <<line-names>> || repeat(<<positive-integer>>, <<line-names>>) ]+
+		<dfn>&lt;line-name-list></dfn> = [ <<line-names>> | repeat(<<positive-integer>>, <<line-names>>) ]+
 	</pre>
 
 	<p>Where: