Add python3 wheel for six.

Bug: 898348
Change-Id: I3abe58863f85f5ca3abf0a5bb00bb969d775ad22
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225928
Auto-Submit: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Cr-Commit-Position: refs/heads/master@{#775277}

.vpython3

@@ -26,3 +26,7 @@ python_version: "3.8"
 
 # TODO(https://crbug.com/898348): Add in necessary wheels as Python3 versions
 # become available.
+wheel: <
+  name: "infra/python/wheels/six-py2_py3"
+  version: "version:1.10.0"
+>