title: NameError: name 'Usuario' is not defined
body: <p>I have this error in django when i try to do "makemigrations"</p>
  
  <p>Code:</p>
  
  <pre><code>from django.db import models
  from django.contrib.auth.models import User
  
  # Create your models here.
  
  class Usuario(models.Model):
      user = models.OneToOneField(User)
      amigos = models.ManyToManyField(Amigo)
  
  
  
  class Amigo(models.Model):  
      usuarios = models.ForeignKey(Usuario)
  
  
  
  class Regalo(models.Model):
      nombre = models.CharField(max_length=100)
      enlace_compra = models.CharField(max_length=200)
      amigo_encargado = models.OneToOneField(User)
  </code></pre>
  
  <p>Sorry, my english is very poor and I use translate.</p>