Add pylint 2.6.0 to depot_tools.

This is the latest version, which supports Python 3 only.

Bug: 1123433
Change-Id: I7516ed52d64f38f8214c6295e9ad3d08a98e2b4d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2473704
Auto-Submit: Owen Rodley <orodley@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>

pylint-2.6

+#!/usr/bin/env vpython3
+# Copyright 2019 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.
+
+# Note: We use tags here instead of refs because refs will always hit the
+# network to see if there are any updates.
+
+# [VPYTHON:BEGIN]
+# # Third party dependencies.  These are only listed because pylint itself needs
+# # them.  Feel free to add/remove anything here.
+#
+# wheel: <
+#   name: "infra/python/wheels/futures-py2_py3"
+#   version: "version:3.1.1"
+# >
+# wheel: <
+#   name: "infra/python/wheels/isort-py2_py3"
+#   version: "version:4.3.4"
+# >
+# wheel: <
+#   name: "infra/python/wheels/mccabe-py2_py3"
+#   version: "version:0.6.1"
+# >
+# wheel: <
+#   name: "infra/python/wheels/six-py2_py3"
+#   version: "version:1.12.0"
+# >
+# wheel: <
+#   name: "infra/python/wheels/toml-py3"
+#   version: "version:0.10.1"
+# >
+# wheel: <
+#   name: "infra/python/wheels/wrapt/${vpython_platform}"
+#   version: "version:1.10.11"
+# >
+# wheel: <
+#   name: "infra/python/wheels/lazy-object-proxy/${vpython_platform}"
+#   version: "version:1.4.3"
+# >
+#
+# # Pylint extensions.
+#
+# wheel: <
+#   name: "infra/python/wheels/pylint-quotes-py2_py3"
+#   version: "version:0.1.8"
+# >
+#
+# # Pylint dependencies.
+#
+# wheel: <
+#   name: "infra/python/wheels/astroid-py3"
+#   version: "version:2.4.2"
+# >
+# wheel: <
+#   name: "infra/python/wheels/pylint-py3"
+#   version: "version:2.6.0"
+# >
+#
+# [VPYTHON:END]
+
+import sys
+
+import pylint_main
+
+sys.exit(pylint_main.main(sys.argv[1:]))