bigtable: Fix branding in cbt help
bigtable: Fix branding in cbt help

Change-Id: If16ab4a3050e65934a3edb3233a899f90ef98cdb
Reviewed-on: https://code-review.googlesource.com/c/37550
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Gary Elliott <d49662846a332c09d32ce16a761e8169b9defdba@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go