autotest: update header to python 3

BUG=None
TEST=CQ

Change-Id: I130f248e21a0485ea0b89f38784f6716c04eb001
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/3563685
Reviewed-by: Derek Beckett <dbeckett@chromium.org>
Feels: Derek Beckett <dbeckett@chromium.org>
Tested-by: Kshitij Shah <tij@google.com>
Feels: Kshitij Shah <tij@google.com>
Commit-Queue: Kshitij Shah <tij@google.com>
diff --git a/client/common_lib/cros/interactive_xmlrpc_server.py b/client/common_lib/cros/interactive_xmlrpc_server.py
index f5f2534..17e87b6 100755
--- a/client/common_lib/cros/interactive_xmlrpc_server.py
+++ b/client/common_lib/cros/interactive_xmlrpc_server.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 
 # Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be