title: $el.find(...).iCheck is not a function
body: <p>I have use example on surveyJs for icheck, but why is error message appears as </p>
  
  <blockquote>
    <p>$el.find(...).iCheck is not a function</p>
  </blockquote>
  
  <p>, I checked that JQuery and icheck library have been added into this project and page loaded before calling iCheck function. </p>
  
  <p><a href="http://surveyjs.org/examples/react/custom-widget-icheck/" rel="nofollow noreferrer">http://surveyjs.org/examples/react/custom-widget-icheck/</a></p>
  
  <pre><code>import { iCheck } from 'icheck';
   var radioGroupWidget = {
   name: "icheck",
      isFit : function(question) { return question["renderAs"] === 'icheck'; },
      isDefaultRender: true,
      afterRender: function(question, el) {
          var $el = $(el);
          var select = function() {
            $el.find("input[value=" + question.value + "]").iCheck('check');
          }
          $el.find('input').iCheck({
            checkboxClass: 'iradio_square-blue',
            radioClass: 'iradio_square-blue'
          });
          $el.find('input').on('ifChecked', function(event){
            question.value = event.target.value;
          });
          question.valueChangedCallback = select;
          select();
      },
      willUnmount: function(question, el) {
          var $el = $(el);
          $el.find('input').iCheck('destroy');
      }
   }
  CustomWidgetCollection.Instance.addCustomWidget(radioGroupWidget);
  </code></pre>