Bump minimum required cmake to 3.12

Author: maflcko

CMakeLists.txt

@@ -2,7 +2,7 @@
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-cmake_minimum_required(VERSION 3.8)
+cmake_minimum_required(VERSION 3.12)
 
 project("Libmultiprocess" CXX)
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)