title: Field value not persisted after import
body: <p><strong>Model.py</strong></p>
  <pre><code>class Order(models.Model):
      customerID =  models.CharField(max_length=300, blank=True, null=True)
      osm_bol = models.CharField(max_length=300, blank=True, null=True)
      .....
      .....
      def __str__(self):
          return self.customerID 
  </code></pre>
  <p><strong>Resouces.py</strong></p>
  <pre><code>class NewOrders(resources.ModelResource):
      osm_bol = Field(attribute='osm_bol', column_name='Client Track ID')
      class Meta:
          model = Order
          fields = ('osm_bol')
  </code></pre>
  <p><strong>Exel Sheet Column</strong>
  <a href="https://i.stack.imgur.com/qia8J.png" rel="nofollow noreferrer">This is the Column that i want to import in my model</a></p>
  <p><strong>Problem</strong>
  the problem is i have the column name &quot;Client Track ID&quot; but in my model the name of attribute is &quot;osm_bol&quot; for the same field. when i import the file it shows nothing in &quot;osm_bol&quot; field. i mean its shows empty field. how can i fix it?</p>