Fix ERF.PRECISE help page

Change-Id: I6ba9feabe55701c902fc95a1fc41fe9455e27a8c
Reviewed-on: https://gerrit.libreoffice.org/13471
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>