[css-fonts-5] Fix link

Author: fantasai

css-fonts-5/Overview.bs

@@ -164,7 +164,7 @@ the 'size-adjust' descriptor</h3>
 	Consequently,
 	any values derived from font metrics
 	(such as ''ex'' and ''ch'' units,
-	or the ''text-underline-thickness/from-font'' value of 'text-underline-thickness')
+	or the ''text-decoration-thickness/from-font'' value of 'text-decoration-thickness')
 	are also affected when sourced from this font.
 	However, the [=computed value|computed=] 'font-size'
 	(and thus any values that derive from it,