bump mac os min version to 10.15 for xpress

Author: lperron

.bazelrc

@@ -23,8 +23,8 @@ build --enable_platform_specific_config
 
 build:linux --cxxopt="-std=c++17" --cxxopt=-Wno-sign-compare
 build:linux --host_cxxopt="-std=c++17" --cxxopt=-Wno-sign-compare
-build:macos --cxxopt="-std=c++17"  --features=-supports_dynamic_linker --cxxopt=-Wno-sign-compare --macos_minimum_os=10.13
-build:macos --host_cxxopt="-std=c++17" --features=-supports_dynamic_linker --cxxopt=-Wno-sign-compare --macos_minimum_os=10.13
+build:macos --cxxopt="-std=c++17"  --features=-supports_dynamic_linker --cxxopt=-Wno-sign-compare --macos_minimum_os=10.15
+build:macos --host_cxxopt="-std=c++17" --features=-supports_dynamic_linker --cxxopt=-Wno-sign-compare --macos_minimum_os=10.15
 build:windows --cxxopt="/std:c++20"
 build:windows --host_cxxopt="/std:c++20"