inotify-tools: fix license

No specific GPL version is declared, so it defaults to "any version
ever published", as clause 9 of the GPLv2 states.

Fixes a05a1cc1.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>