Ensure signal handler takes correct arguments

Author: j4mie

Diff for: django_dbq/management/commands/worker.py

@@ -87,7 +87,7 @@ def init_signals(self):
         signal.signal(signal.SIGQUIT, self.shutdown)
         signal.signal(signal.SIGTERM, self.shutdown)
 
-    def shutdown(self):
+    def shutdown(self, signum, frame):
         self.alive = False
 
     def run(self):