chore: update TUF spec version to 1.0.31 (#393)
chore: update TUF spec version to 1.0.31 (#393)

Fixes #391; see that issue for justification.

Signed-off-by: Zachary Newman <395df8f7c51f007019cb30201c49e884b46b92fa@znewman.net>

Signed-off-by: Zachary Newman <395df8f7c51f007019cb30201c49e884b46b92fa@znewman.net>
theupdateframework/go-tuf