luci-mod-system: use proper CSS class for map description

Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit 90990df3b6)

modules/luci-mod-system/htdocs/luci-static/resources/view/system/crontab.js

@@ -22,7 +22,7 @@ return view.extend({
 	render: function(crontab) {
 		return E([
 			E('h2', _('Scheduled Tasks')),
-			E('p', {},
+			E('p', { 'class': 'cbi-section-descr' },
 				_('This is the system crontab in which scheduled tasks can be defined.') +
 				_('<br/>Note: you need to manually restart the cron service if the crontab file was empty before editing.')),
 			E('p', {}, E('textarea', { 'style': 'width:100%', 'rows': 10 }, [ crontab != null ? crontab : '' ]))