bump the required CMake version to 3.16 (#32)

The latest CI pipelines have updated to CMake 4.0, which drops
support for CMake 3.5 and before.  Updating the required CMake
version to 3.16 should still support older operating systems,
but allow the latest CI pipelines to run.

Author: bashbaug

CMakeLists.txt

@@ -4,7 +4,7 @@
 
 # Note: cmake 3.7 is needed to use OpenCL::OpenCL.
 # Older versions may work by explicitly specifying OpenCL_INCLUDE_DIRS and OpenCL_LIBRARIES.
-cmake_minimum_required(VERSION 3.7 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.16 FATAL_ERROR)
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 
 set(CMAKE_CXX_STANDARD 11)