README: fix typo
README: fix typo

Change-Id: Icfdeee43836d3c61312a3ef1508f8678f84a9cb5
Reviewed-on: https://code-review.googlesource.com/16110
Reviewed-by: Chris Broadfoot <0c2851a4f8ab4aa5606e69c0757771dd13dbe686@google.com>

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