Fix help string typo.
Fix help string typo.

Bug:
Change-Id: Id7509ae08bc09c6cb291f29b55c60d6d96e79121
Reviewed-on: https://chromium-review.googlesource.com/721359
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: David Benjamin <348b1b6801801c3d890b2e1589a8e36441d09fdc@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools