[css-grid-2] Fix grammar source. Fixes w3c#2917.

Author: tabatkins

css-align-3/Overview.bs

@@ -1787,7 +1787,7 @@ Self-Alignment Shorthand: the 'place-items' property</h3>
 
 	<pre class="propdef">
 	Name: place-items
-	Value: <'align-items'> <'justify-items'>?
+	Value: <<'align-items'>> <<'justify-items'>>?
 	Initial: see individual properties
 	Applies to: all elements
 	Inherited: no

css-grid-2/Overview.bs

@@ -129,7 +129,7 @@ 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( [ <<positive-integer>> | auto-fill ], <<line-names>>+)
 	</pre>
 
 	The <<name-repeat>> variant of the ''repeat()'' notation