knot: add PKG_LICENSE tag

Signed-off-by: Daniel Salzman <daniel.salzman@nic.cz>
knot: update to 1.5.2.

Signed-off-by: Daniel Salzman <daniel.salzman@nic.cz>
knot: update to 1.5.3.

Signed-off-by: Daniel Salzman <daniel.salzman@nic.cz>
Merge pull request #313 from salzmdan/master

knot: update to 1.5.3