[sudo-workers] Replace (ALL) with (ALL:ALL) in sudoers file

[Justin Spencer]

Justification: Allow "sudo -g anyone" and "sudo -u anyone -g anytwo"

When only the user (ALL) is specified explicitly, and the group is 
implied, only sudo -u works. Specifying both the user and group, like 
(ALL:ALL), is required to:

1. Use sudo -g by itself (with no -u user)
2. Use sudo -u and -g together, with a -g group that is different from 
the -u user's primary group

Diff: https://github.com/sudo-project/sudo/pull/124/files