Doc: Fix warning about deprecated \bold usage

  warning: '\bold' is deprecated. Use '\b'

Change-Id: If377a5ecba4488b8d4e368164c67bd0fb9dcbac1
Reviewed-by: Sze Howe Koh <szehowe.koh@gmail.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>