package/cmake: bump to version 3.18.6

Update hash of Copyright.txt (year updated and Qt Company Ltd. added:
https://gitlab.kitware.com/cmake/cmake/-/commit/1edc4a8a7e759c4047dd1a1b9864b34f6cb4cc50
https://gitlab.kitware.com/cmake/cmake/-/commit/f8c505d4b30aa636b013486913591060b2040716

)

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>