[css-grid] => 'behaves as auto'. Fixes #2367.

Author: tabatkins

css-grid-1/Overview.bs

@@ -3777,7 +3777,7 @@ Resolve Intrinsic Track Sizes</h3>
 					the item’s 'min-width' or 'min-height' value
 					(whichever matches the relevant axis)
 					as its specified size
-					if its specified size ('width' or 'height', whichever matches the relevant axis) is ''width/auto'',
+					if its computed size ('width' or 'height', whichever matches the relevant axis) [=behaves as 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),