[css-grid] Fix ambiguity reported in #507.

css-grid/Overview.bs

@@ -3858,7 +3858,9 @@ Resolve Intrinsic Track Sizes</h3>
 					to the maximum of its items’ <dfn noexport>min-size contributions</dfn>:
 					the value specified by its respective 'min-width' or 'min-height' properties
 					(whichever matches the relevant axis)
-					if the specified size is ''width/auto'',
+					if the specified size
+					('width' or 'height', whichever matches the relevant axis)
+					is ''width/auto'',
 					or else the item’s <a>min-content contribution</a>.
 
 					Note: For items with a specified minimum size of ''min-width/auto'' (the initial value),