ui: fix typo & add stylus style (#1195)

packages/ui-default/templates/contest_edit.html

@@ -200,7 +200,7 @@
             <div style="display: none" class="contest-rule-settings contest-rule--oi contest-rule--ioi contest-rule--ledo contest-rule--strictioi">
             {{ form.form_text({
               columns:4,
-              label:'Flexable Duration',
+              label:'Flexible Duration',
               name:'contestDuration',
               placeholder:_('(leave blank if none)'),
               value:tdoc.duration|default(''),