Explicitly run everything with python3

R=aravindvasudev@google.com, gavinmak@google.com

Change-Id: Iaa5e960c6226dea3a0814c7cb778d952eafb1502
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3525960
Reviewed-by: Gavin Mak <gavinmak@google.com>
Reviewed-by: Aravind Vasudevan <aravindvasudev@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
diff --git a/metrics.py b/metrics.py
index 5e3a935..c5b86b6 100644
--- a/metrics.py
+++ b/metrics.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright (c) 2018 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
@@ -62,7 +62,7 @@
       self._initialized = True
       return
 
-    # We are running on a bot. Ignore config and collect metrics. 
+    # We are running on a bot. Ignore config and collect metrics.
     if metrics_utils.REPORT_BUILD:
       self._config = {
         'is-googler': True,