Some documentation uses the old default branch name `master`.
But `master` in crashpad repo is a very old branch and has been
superseded with `main`.
Change-Id: I368c829fde2d29b3f14aa14185bfc97d546bf340
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/3787194
Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Mark Mentovai <mark@chromium.org>