switch Sliver.ip from IpAddressField to GenericIPAddressField
diff --git a/plstackapi/core/models/sliver.py b/plstackapi/core/models/sliver.py
index 82359ef..2eabf23 100644
--- a/plstackapi/core/models/sliver.py
+++ b/plstackapi/core/models/sliver.py
@@ -15,7 +15,7 @@
 class Sliver(PlCoreBase):
     instance_id = models.CharField(max_length=200, help_text="Nova instance id")    
     name = models.CharField(max_length=200, help_text="Sliver name")
-    ip = models.IPAddressField(help_text="Sliver ip address", blank=True, null=True)
+    ip = models.GenericIPAddressField(help_text="Sliver ip address", blank=True, null=True)
     flavor = models.ForeignKey(Flavor, related_name='slivers')
     image = models.ForeignKey(Image, related_name='slivers')
     key = models.ForeignKey(Key, related_name='slivers')