ncdu: Update to version 1.20

ncdu: Update to version 1.20

- Update from version 1.18.1 to 1.20
- Update of rootfile not required
- Changelog
    1.20
	- Revert default color scheme back to 'off'
	- Rewrite man page in mdoc, drop pod2man dependency
    1.19
	- Fix typo in --exclude-from argument
	- Add --(enable|disable)-natsort options
	- Add indicator to apparent size/disk usage selection in the footer

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>