Bump version 1.3.8

Change-Id: Id41c3531562d9b8d8ceb303051955bbac814e086
Reviewed-on: http://review.couchbase.org/38107
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>