title: Select2 placeholder not working in rails app with hidden_field
body: <p>Haml: </p>
  
  <pre><code> .form-group
              = f.hidden_field :gender, :id =&gt; 'select2', :style =&gt; "width:100%; height: 40px"
  </code></pre>
  
  <p>JS: </p>
  
  <pre><code> $("#select2").select2({
      createSearchChoice: function (term, data) {
        if ($(data).filter(function () {
              return this.text.localeCompare(term) === this.text;
            }).length === 0) {
          return {
            id: term,
            text: term
          };
        }
        console.log('SELECT2', $("#select2").data.text);
      },
      placeholder: "Enter custom gender or select one below",
      multiple: false,
      data: [{
        id: 'male',
        text: 'male'
      }, {
        id: 'female',
        text: 'female'
      }, {
        id: 'custom',
        text: 'custom'
      }]
  });
  </code></pre>
  
  <p>Select2 is doing everything I need now, but the placeholder is not showing on my view. Any help, much appreciated. </p>