Merge pull request #3013 from OpenMW/macos_target_fix

Resolve 'shared_timed_mutex' is unavailable: introduced in macOS 10.12

CI/before_script.osx.sh

@@ -16,7 +16,7 @@ cmake \
 -D CMAKE_CXX_FLAGS="-std=c++11 -stdlib=libc++" \
 -D CMAKE_C_FLAGS_RELEASE="-g -O0" \
 -D CMAKE_CXX_FLAGS_RELEASE="-g -O0" \
--D CMAKE_OSX_DEPLOYMENT_TARGET="10.9" \
+-D CMAKE_OSX_DEPLOYMENT_TARGET="10.12" \
 -D CMAKE_BUILD_TYPE=RELEASE \
 -D OPENMW_OSX_DEPLOYMENT=TRUE \
 -D BUILD_OPENMW=TRUE \