Bump OSX deployment target to 10.15

CMakeLists.txt

@@ -9,7 +9,7 @@ cmake_minimum_required(VERSION ${REQUIRED_CMAKE_VERSION})
 option(BUILD_SHARED_LIBS "Build external projects as shared libraries." ON)
 option(CMAKE_VERBOSE_MAKEFILE "Build with verbose Makefile output." OFF)
 set(CMAKE_CXX_STANDARD 17 CACHE STRING "Set the C++ standard the dependencies should be build with.")
-set(CMAKE_OSX_DEPLOYMENT_TARGET 10.9 CACHE STRING "Set the minimum OSX deployment target version")
+set(CMAKE_OSX_DEPLOYMENT_TARGET 10.15 CACHE STRING "Set the minimum OSX deployment target version")
 set(CMAKE_OSX_ARCHITECTURES x86_64 CACHE STRING "Set the architecture the binaries for OSX should be built for")
 set(CMAKE_INSTALL_MESSAGE NEVER CACHE STRING "Set the verbosity level for the install messages")
 set(BOOST_PARALLEL_JOBS 1 CACHE STRING "Set the Boost.Build parallel jobs")