bisect-kit: switch to python3

BUG=b:140004822
TEST=test manually

Change-Id: Id7e309beceae3d0af40da077acfbb49ed8e240c6
diff --git a/switch_git.py b/switch_git.py
index 3868578..6be2f85 100755
--- a/switch_git.py
+++ b/switch_git.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 # Copyright 2017 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be