require CMake 3.8 to understand CXX17 flags - thanks @leeanne2 for reporting (#285)

Author: slayoo

CMakeLists.txt

@@ -4,7 +4,7 @@
 # Author: Sylwester Arabas                                                                         #
 ####################################################################################################
 
-cmake_minimum_required(VERSION 3.4...3.18)
+cmake_minimum_required(VERSION 3.8)  # CXX17
 
 if (NOT EXISTS "${CMAKE_SOURCE_DIR}/gitmodules/pybind11/include/pybind11/pybind11.h" )
   message(FATAL_ERROR "git submodules not initialised.\n Please run `git submodule update --init`")