respect the virtualenv by using /usr/bin/env

Signed-off-by: S.Çağlar Onur <caglar@10ur.org>
diff --git a/planetstack/syndicate_observer/steps/sync_volumeslice.py b/planetstack/syndicate_observer/steps/sync_volumeslice.py
index 0fc6d4d..63b5e53 100644
--- a/planetstack/syndicate_observer/steps/sync_volumeslice.py
+++ b/planetstack/syndicate_observer/steps/sync_volumeslice.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 
 import os
 import sys