[bot_update] fix Property default to be actual JSON.
[bot_update] fix Property default to be actual JSON.

R=8400006a9338a0893dca0101ad49838955bd6b2c@chromium.org

Bug:
Change-Id: I18eb355282f2efc067a6dc70e1136f9a49d3488a
Reviewed-on: https://chromium-review.googlesource.com/494306
Reviewed-by: Daniel Jacques <8400006a9338a0893dca0101ad49838955bd6b2c@chromium.org>
Commit-Queue: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools