uploader: fix `auth revoke` help suggestion (#2842)
uploader: fix `auth revoke` help suggestion (#2842)

Summary:
The correct invocation is `auth revoke`, not `--auth_revoke`, which was
a vestige of a previous formulation.

wchargin-branch: uploader-auth-revoke-text
tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard