sfw: Change env path

I don't know what systems have env(1) in /bin but at least on Ubuntu
it's in /usr/bin/env.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/openbmc-sfw b/openbmc-sfw
index a6f5926..cd439e6 100755
--- a/openbmc-sfw
+++ b/openbmc-sfw
@@ -1,4 +1,4 @@
-#!/bin/env python
+#!/usr/bin/env python
 
 import argparse
 import requests