title: validators = [MinValueValidator] does not work in Django
body: <p>I want to set the minimum value for FloatField in Django so that the form field does not accept negative value. In case of Integers I changed the datatype to PositiveIntegerField but minimum value is not working in case of float field. </p>
  
  <pre><code>from django.core.validators import MaxValueValidator, MinValueValidator
  
  max_discount = models.FloatField( verbose_name=u'Maximum Discount', validators = [MinValueValidator(0.0)])
  </code></pre>