update calendar selector to work with the latest octobercms versions

formwidgets/calendarselector/partials/_selector.htm

@@ -3,7 +3,7 @@
         <thead>
         <tr>
             <th class="list-checkbox">
-                <div class="checkbox custom-checkbox nolabel">
+                <div class="checkbox nolabel">
                     <input type="checkbox" id="checkboxAll" />
                     <label for="checkboxAll"></label>
                 </div>