Revert back to SIGQUIT.

In the previous commit, I changed that signal from SIGQUIT to SIGINT without
apparent reason. Either should work as they are meant to be used the same way
for the same purpose. Still, there was no reason to change so let's revert.

Author: adk-swisstopo

gunicorn/arbiter.py

@@ -394,7 +394,7 @@ def stop(self, graceful=True):
 
         if not graceful or self.cfg.quick_shutdown_timeout > 0:
             deadline = time.time() + self.cfg.quick_shutdown_timeout
-            self.kill_workers(signal.SIGINT)
+            self.kill_workers(signal.SIGQUIT)
             self.sleep_until(deadline)
 
         self.kill_workers(signal.SIGKILL)