vpython doesn't parse shebang. If python version is not explicitly set
in vpython file, version 2 will be used. pylint 2.6 requires py3.

R=dpranke@google.com

Bug: 1242737
Change-Id: I21a3c4b26c24860b4c8fd07c6d5cc6d5149af2fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3120321
Auto-Submit: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>