Update minimum CMake version

[mratzloff]

CMake 3.25.2 gives this deprecation warning:

CMake Deprecation Warning at [tinyformat]/CMakeLists.txt:21 (cmake_minimum_required):
Compatibility with CMake < 2.8.12 will be removed from a future version of
CMake.

Update the VERSION argument value or use a ... suffix to tell
CMake that the project does not need compatibility with older versions.