fix sliver.all_ips() throwing traceback
diff --git a/planetstack/core/models/sliver.py b/planetstack/core/models/sliver.py
index 610a65e..3804dba 100644
--- a/planetstack/core/models/sliver.py
+++ b/planetstack/core/models/sliver.py
@@ -124,7 +124,7 @@
 
     def all_ips(self):
         ips={}
-        for ns in self.networksliver_set.all():
+        for ns in self.networkslivers.all():
            ips[ns.network.name] = ns.ip
         return ips