CMake file might be outdated soon

[PrometheusPi]

If I compile PIConGPU with ISAAC enabled in HZDR hemera, I get the following deprecation warning:

.../lib/isaac/lib/cmake/ISAAC/ISAACConfig.cmake:30 (cmake_policy):
  The OLD behavior for policy CMP0048 will be removed from a future version
  of CMake.

  The cmake-policies(7) manual explains that the OLD behaviors of all
  policies are deprecated and that a policy should be set to OLD only under
  specific short-term circumstances.  Projects should be ported to the NEW
  behavior and not rely on setting a policy to OLD.
Call Stack (most recent call first):
  CMakeLists.txt:392 (find_package)

This most likely needs to be fixed in the future.