package/rng-tools: update help text website reference
We switched to new upstream since commit f9e9c6349afe0
("package/rng-tools: bump to 6.7"). Update the website URL as well.
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>