title: django-rest-auth error - save() takes 1 positional argument but 2 were given
body: <p>I'm using django-rest-auth with a custom user model, registration view and serializer. What I'm trying to achieve is an email login instead of username. The api view shows correctly but when I post, I get the error:</p>
  
  <pre><code>TypeError at /rest-auth/registration/
  save() takes 1 positional argument but 2 were given
  </code></pre>
  
  <p>this is the traceback: <a href="http://dpaste.com/2FR3DZY" rel="nofollow noreferrer">http://dpaste.com/2FR3DZY</a></p>
  
  <p>serializer.py</p>
  
  <pre><code>class CustomUserSerializer(serializers.ModelSerializer):
  """Serializer for User objects."""
  
      class Meta:
          model = models.User
          fields = ('id', 'email', 'name', 'password')
          extra_kwargs ={'password': {'write_only': True}}
  
      def create(self, validated_data):
          """Create and return a new User."""
  
          user = models.User(
              email=validated_data['email'],
              name=validated_data['name'] 
          )
  
          user.set_password(validated_data['password'])
          user.save()
  
          return user
  </code></pre>
  
  <p>views.py</p>
  
  <pre><code>class CustomRegistrationsView(RegisterView):
      serializer_class = CustomUserSerializer
  </code></pre>
  
  <p>urls.py</p>
  
  <pre><code>path('rest-auth/registration/', CustomRegistrationsView.as_view(), name='rest_register'),   
  path('rest-auth/', include('rest_auth.urls')),
  </code></pre>
  
  <p>models.py</p>
  
  <pre><code>class UserManager(BaseUserManager):
  """Helps Django work with our custom user model."""
  
      def create_user(self, email, name, password=None):
          """Creates a new user object."""
  
          if not email:
              raise ValueError('Users must have an email address.')
  
          email = self.normalize_email(email)
          user = self.model(email=email, name=name)
  
          user.set_password(password)
          user.save(using=self._db)
  
          return user
  
      def create_superuser(self, email, name, password):
          """Creates and saves a new superuser with given details."""
  
          user = self.create_user(email, name, password)
  
          user.is_superuser = True
          user.is_staff = True
  
          user.save(using=self._db)
  
          return user
  
  class User(AbstractBaseUser, PermissionsMixin):
      """Represents a "user" inside our system."""
  
      email = models.EmailField(max_length=255, unique=True)
      name = models.CharField(max_length=255)
      is_active = models.BooleanField(default=True)
      is_staff = models.BooleanField(default=False)
  
      objects = UserManager()
  
      USERNAME_FIELD = 'email'
      REQUIRED_FIELDS = ['name']
  
      def get_full_name(self):
          """Used to get a users full name."""
  
          return self.name
  
      def get_short_name(self):
          """Used to get a users short name."""
  
          return self.name
  
      def __str__(self):
          """Django uses this when it needs to convert the object to a string"""
  
          return self.email
  </code></pre>
  
  <p>Can anyone advise?</p>