[css-ui] Closing missing parenthesis

Author: mrego

css-ui-4/Overview.bs

@@ -1329,7 +1329,7 @@ Shape of the insertion caret: 'caret-shape'</h4>
 		<dt><dfn>underscore</dfn>
 		<dd>
 			The UA must render the [=insertion caret=]
-			as a thin line <a>under</a> (as defined in [[!CSS-WRITING-MODES-3]]
+			as a thin line <a>under</a> (as defined in [[!CSS-WRITING-MODES-3]])
 			the next <a>visible character</a> following the insertion point.
 			If there is no <a>visible character</a> after the insertion point,
 			the UA must render the caret after the last <a>visible character</a>.