title: TypeError: __init__() got an unexpected keyword argument 'show_preview'
body: <p>I am getting this error in Django 1.9</p>
  
  <pre><code>in PostForm
      content = forms.CharField(widget=PagedownWidget(show_preview=False))
  TypeError: __init__() got an unexpected keyword argument 'show_preview'
  </code></pre>
  
  <p><strong>forms.py</strong></p>
  
  <pre><code>class PostForm(forms.ModelForm):
      content = forms.CharField(widget=PagedownWidget(show_preview=False))
      publish = forms.DateField(widget=forms.SelectDateWidget)
      class Meta:
          model = Post
          fields = [
              "title",
              "content",
              "image",
              "draft",
              "publish",
          ]
  </code></pre>
  
  <p>The dependencies installed in the virtual environment
  <strong>$ pip freeze</strong></p>
  
  <pre><code>certifi==2019.11.28
  Django==1.9
  django-crispy-forms==1.8.1
  django-filter==2.2.0
  django-markdown-deux==1.0.5
  django-pagedown==2.0.3
  djangorestframework==3.11.0
  Markdown==3.1.1
  markdown2==2.3.1
  olefile==0.46
  Pillow==6.2.1
  </code></pre>