title: django-autocomplete-light, widget attributes, no placeholder visible
body: <p>I've implemented autocomplete in my form: <br><br><code>related_groups = forms.ModelChoiceField(
          queryset=UserGroup.objects.all(),
          widget=autocomplete.ModelSelect2Multiple(
              url='groups-autocomplete',
              attrs={
                  'data-placeholder': 'Autocomplete ...',
                  'data-minimum-input-length': 2,
              },
          )
      )</code>
      <br><br>
  Generally, autosuggesting works but the placeholder and minimum input lenght don't (groups-autocomplete is my alias to my view).
  Are these fields properly written here? I found such an example in official tutorial available <a href="http://django-autocomplete-light.readthedocs.io/en/master/tutorial.html" rel="nofollow noreferrer">here</a>: <br> . <br> Am i missing something here? I'm really confused about that.</p>