[css-grid] Use the term 'stretch fit' to avoid some wordiness.

Author: tabatkins

css-grid/Overview.bs

@@ -1258,9 +1258,9 @@ Implied Minimum Size of Grid Items</h3>
 	that have a <a lt="fixed sizing function">fixed</a> <a>max track sizing function</a>,
 	its <a>specified size</a> and <a>content size</a> in that dimension
 	(and the input to the <a>transferred size</a> in the other dimension)
-	are further clamped to less than or equal to the size necessary
-	to fit its margin box within the resulting <a>grid area</a> (flooring at zero),
-	so as to prevent the <a>automatic minimum size</a> from forcing overflow of its fixed-size grid area.
+	are further clamped to less than or equal to the <a>stretch fit</a>
+	the <a>grid area</a>’s size
+	(so as to prevent the <a>automatic minimum size</a> from forcing overflow of its fixed-size grid area).
 
 	<div class="note" id="min-size-opt">
 		Note that while a content-based minimum size is often appropriate,