[css-grid] Clean up dangling pointer noted in #638

Author: fantasai

css-grid/Overview.bs

@@ -3564,7 +3564,7 @@ Grid Container Baselines</h3>
 			the grid container's first (last) baseline set
 			is <a lt="generate baselines">generated</a> from
 			the <a>alignment baseline</a> of the first (last) such <a>grid item</a> (in row-major <a>grid order</a>).
-			If the item has no <a>alignment baseline</a> in that axis,
+			If the item has no <a>alignment baseline</a> in the grid's inline axis,
 			then one is first <a lt="synthesize baselines">synthesized</a>
 			from its border edges.