fix extract_derivatives command

pandora/archive/management/commands/extract_derivatives.py

@@ -1,13 +1,16 @@
 # -*- coding: utf-8 -*-
 # vi:si:et:sw=4:sts=4:ts=4
+import os
+from optparse import make_option
+
 from django.core.management.base import BaseCommand
 from django.conf import settings
-import os
 
 import monkey_patch.models
 from ... import models
 from ...tasks import extract_derivatives
 
+
 class Command(BaseCommand):
     """
     """