[kdenlive] Build failing at CI

[Albert Astals Cid]

See 
https://build.kde.org/job/kdenlive%20master%20kf5-qt5/PLATFORM=Linux,compiler=gcc/189/console

My understanding is that the error is 

00:01:34.473 CMake Error at CMakeLists.txt:13 (cmake_policy):
00:01:34.473   Policy "CMP0063" is not known to this version of CMake.

Someone suggested you should wrap that command in a 

if(POLICY CMP0063)
endif()

block.

Can someone verify that it still works and commit it?

Thanks,
  Albert