_OLD_VRUBY_PATH doesn't separate paths

[joefiorini]

Just noticed this when running env:

_OLD_VRUBY_PATH=/usr/local/opt/fzf/bin/usr/local/bin/usr/bin/bin/usr/sbin/sbin

Those paths should be separated with ":" just like the normal PATH variable. Otherwise this could cause problem when we try to restore the PATH on deactivate.