transmission: update to version 4.0.1

transmission: update to version 4.0.1

This is a major release, both in numbering and in effort! It's been in
active development for over a year and has a huge list of changes --
over a thousand commits -- since Transmission 3.00.

For more information about the release see
https://github.com/transmission/transmission/releases/tag/4.0.0
https://github.com/transmission/transmission/releases/tag/4.0.1

Signed-off-by: Daniel Golle <daniel@makrotopia.org>