Added max CMake version 3.16.

This should resolve CMake warnings.

Author: Lastique

CMakeLists.txt

@@ -7,7 +7,7 @@
 # NOTE: CMake support for Boost.Filesystem is currently experimental at best
 #       and the interface is likely to change in the future
 
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 3.5...3.16)
 project(BoostFilesystem VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)
 
 include(CheckCXXSourceCompiles)

test/test_cmake/CMakeLists.txt

@@ -6,7 +6,7 @@
 # NOTE: This does NOT run the unit tests for Boost.Filesystem.
 #       It only tests, if the CMakeLists.txt file in it's root works as expected
 
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 3.5...3.16)
 
 project(BoostFilesystemCMakeSelfTest)