[depot tools] Update six version.

Change-Id: Ic776edca9a399b4667451e702388c2747d397f9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3738368
Auto-Submit: Joanna Wang <jojwang@chromium.org>
Reviewed-by: Aravind Vasudevan <aravindvasudev@google.com>
Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>

third_party/six/LICENSE.txt

-Copyright (c) 2010-2014 Benjamin Peterson
+Copyright (c) 2010-2020 Benjamin Peterson
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of
 this software and associated documentation files (the "Software"), to deal in

third_party/six/README.chromium

 URL: https://pypi.python.org/pypi/six
-Version: 1.8.0
+Version: 1.10.0
 License: MIT
 License File: LICENSE.txt