Fixed grammar error

Change-Id: Ibe24197f309b756fcc3c9d17abb738e67e2b7990
Reviewed-on: https://weave-review.googlesource.com/1760
Reviewed-by: Vitaly Buka <vitalybuka@google.com>
(cherry picked from commit b0efd87c2d06215f55e37f554006e1644483427e)
Reviewed-on: https://weave-review.googlesource.com/1761