[css-align] Per WG resolution, use more 'computes to' rather than 'behaves as' when possible in these properties.

Author: tabatkins

css-align/Overview.bs

@@ -484,11 +484,10 @@ Content Distribution: the 'justify-content' and 'align-content' properties</h2>
 			for 'align-content', the <a>alignment subjects</a> are the <a>flex lines</a>.
 
 			The 'align-content' property applies along the <a>cross axis</a>.
+
 			The 'justify-content' property applies along the <a>main axis</a>,
 			but since flexing in the <a>main axis</a> is controlled by 'flex',
-			''<content-distribution>/stretch'' behaves as ''flex-start''.
-
-			Issue: https://lists.w3.org/Archives/Public/www-style/2015Apr/0247.html
+			''<content-distribution>/stretch'' computes to ''flex-start''.
 
 			See [[!CSS3-FLEXBOX]] for details.