Require CMake 3.5 of higher

This fixes the deprecation warning as reported in #64

Author: mlund

CMakeLists.txt

@@ -6,7 +6,7 @@
 # The full license is in the file LICENSE, distributed with this software. #
 ############################################################################
 
-cmake_minimum_required(VERSION 3.4.3)
+cmake_minimum_required(VERSION 3.5)
 project(pybind11_json)
 
 set(PYBIND11_JSON_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/include)