firewall: use timezone instead of datetime

Using datetime causes a RuntimeWarning because DateTimeField receives a naive
datetime while time zone support is active.

circle/firewall/fw.py

@@ -2,7 +2,7 @@ import re
 import logging
 from collections import OrderedDict
 from netaddr import IPAddress, AddrFormatError
-from datetime import datetime, timedelta
+from datetime import timedelta
 from itertools import product
 
 from .models import (Host, Rule, Vlan, Domain, Record, BlacklistItem,
@@ -11,6 +11,7 @@ from .iptables import IptRule, IptChain
 import django.conf
 from django.db.models import Q
 from django.template import loader, Context
+from django.utils import timezone
 
 
 settings = django.conf.settings.FIREWALL_SETTINGS
@@ -134,7 +135,7 @@ class BuildFirewall:
 
 
 def ipset():
-    week = datetime.now() - timedelta(days=2)
+    week = timezone.now() - timedelta(days=2)
     filter_ban = (Q(type='tempban', modified_at__gte=week) |
                   Q(type='permban'))
     return BlacklistItem.objects.filter(filter_ban).values('ipv4', 'reason')