Fix minor phrasing issues in replica read docblock.

Change-Id: Ia9d515326758e9ea46ccf2bfa95375f2b434d1e1
Reviewed-on: http://review.couchbase.org/27351
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>