raised minimum version of cmake to 3.21

Author: fceller

CMakeLists.txt

@@ -1,6 +1,6 @@
 # -*- mode: CMAKE; -*-
 
-cmake_minimum_required(VERSION 3.9)
+cmake_minimum_required(VERSION 3.21)
 project(velocypack CXX C)
 
 set(CMAKE_CXX_STANDARD 20 CACHE STRING "target C++ standard")