Don't source ~/.naverc if using XDG_CONFIG_HOME
Don't source ~/.naverc if using XDG_CONFIG_HOME

Source it from $XDG_CONFIG_HOME/.naverc instead.

BREAKING CHANGE: This is a breaking change, because a file at ~/.naverc
might not be sourced any more when loading subshells.  Bumps the
rcversion from 3 to 4.

isaacs/nave,isaacs/nave