title: __init__() got an unexpected keyword argument 'min_length'
body: <p>I get the bellow error:</p>
  
  <pre><code>...
  File "/Library/Python/2.7/site-packages/Django-1.11.2-py2.7.egg/django/utils/autoreload.py", line 227, in wrapper
      fn(*args, **kwargs)
    File "/Library/Python/2.7/site-packages/Django-1.11.2-py2.7.egg/django/__init__.py", line 27, in setup
      apps.populate(settings.INSTALLED_APPS)
    File "/Library/Python/2.7/site-packages/Django-1.11.2-py2.7.egg/django/apps/registry.py", line 108, in populate
      app_config.import_models()
    File "/Library/Python/2.7/site-packages/Django-1.11.2-py2.7.egg/django/apps/config.py", line 202, in import_models
      self.models_module = import_module(models_module_name)
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/importlib/__init__.py", line 37, in import_module
      __import__(name)
    File "/Users/luowensheng/Desktop/QIYUN/Project/officialWeb/frontend/models.py", line 93, in &lt;module&gt;
      class User(models.Model):
    File "/Users/luowensheng/Desktop/QIYUN/Project/officialWeb/frontend/models.py", line 97, in User
      phone = models.CharField(min_length=11, max_length=11)
    File "/Library/Python/2.7/site-packages/Django-1.11.2-py2.7.egg/django/db/models/fields/__init__.py", line 1061, in __init__
      super(CharField, self).__init__(*args, **kwargs)
  TypeError: __init__() got an unexpected keyword argument 'min_length'
  </code></pre>
  
  <p>My Model code is below:</p>
  
  <pre><code>class User(models.Model):
      username = models.CharField(max_length=16)
      password = models.CharField(max_length=16)
      real_name = models.CharField(max_length=12)
      phone = models.CharField(min_length=11, max_length=11) # this is the line 97 
      email = models.EmailField()
      qq = models.CharField(max_length=10)
      address = models.CharField(max_length=64)  
      id_card = models.CharField(min_length = 18, max_length=18)
      id_card_img_front = models.CharField(max_length=256)
      id_card_img_back = models.CharField(max_length=256)
      nickname = models.CharField(max_length=16)
      profile = models.CharField(max_length=256)
  </code></pre>
  
  <p>Why I get that error? 
  And by the way if there is a better way to constraint the phone length to <code>11</code>?</p>