package/sudo: bump version to 1.8.31

package/sudo: bump version to 1.8.31

Notice that 1.8.31 fixes a security issue with the non-default pwfeedback
option, but according to the advisory this is not exploitable in 1.8.28:

versions 1.8.26 through 1.8.30 it is not exploitable due to a change in EOF
handling introduced in sudo 1.8.26

https://www.sudo.ws/alerts/pwfeedback.html

Adjust license hash as the copyright year was changed:
-   Copyright (c) 1994-1996, 1998-2019
+   Copyright (c) 1994-1996, 1998-2020

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>