[build] fix shebang for toolchain build scripts

- pakcage_version/package_version.py: python -> python3
- update_pnacl_tool_revision.py: python3 -> vpython3 + python libs

Bug: b/328724250
Change-Id: Iaecfbc5e13eacef23f5c7cd37a5569b6c5b5e7d6
Reviewed-on: https://chromium-review.googlesource.com/c/native_client/src/native_client/+/5426071
Auto-Submit: Junji Watanabe <jwata@google.com>
Reviewed-by: Derek Schuff <dschuff@chromium.org>
Commit-Queue: Derek Schuff <dschuff@chromium.org>
Reviewed-by: Fabian Sommer <fabiansommer@chromium.org>
diff --git a/build/package_version/package_version.py b/build/package_version/package_version.py
index 048d978..eba8918 100755
--- a/build/package_version/package_version.py
+++ b/build/package_version/package_version.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright (c) 2014 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
diff --git a/build/update_pnacl_tool_revisions.py b/build/update_pnacl_tool_revisions.py
index aa17649..8c2ac52 100755
--- a/build/update_pnacl_tool_revisions.py
+++ b/build/update_pnacl_tool_revisions.py
@@ -1,8 +1,19 @@
-#!/usr/bin/python3
+#!/usr/bin/env vpython3
 # Copyright (c) 2013 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+# [VPYTHON:BEGIN]
+# wheel: <
+#   name: "infra/python/wheels/python-dateutil-py3"
+#   version: "version:2.8.1"
+# >
+# wheel: <
+#   name: "infra/python/wheels/six-py3"
+#   version: "version:1.15.0"
+# >
+# [VPYTHON:END]
+
 import argparse
 import collections
 import datetime