changed 'gap' to 'line-grid'

Author: howcom

css3-gcpm/Overview.src.html

@@ -3291,7 +3291,7 @@ <h3>Aligning baselines</h3>
 
 <pre>
 div.multicol { line-height: 15px }
-div.figure { height: 20px; line-box-contain: block inline replaced gap }
+div.figure { height: 20px; line-box-contain: block inline replaced line-grid }
 </pre>
 </div>