libconfuse: bump version

The tag v2.7 is from 2010, no release has been since then and a few
changes have been made, notably a LICENSE file was added.

[Thomas: fix minor typos in commit log.]

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>