fix for sudo tab completion

I'm opening this issue as, apparently, I cannot open a merge request (or I don't know how to).

This should fix issue #2 (closed), when bash-completion is installed, while preserving the old behaviour when it is not.

Replace line in dot.bashrc:

complete -cf sudo

With:

[ -r /usr/share/bash-completion/bash_completion ] || complete -cf sudo

AFAIK the reason for the problem is that bash-completion adds the file /usr/share/bash-completion/completions/sudo which installs a completion handler (complete -F _sudo sudo) which conflicts with complete -cf sudo.