fix macos codecov (#495)
fix macos codecov (#495)

pin back the version of xcode to 10.3 which was the last known version of xcode that doesn't break code coverage.

Signed-off-by: The MathWorks, Inc. <553a03f5161ee6f4083f360816a2718678bbf903@mathworks.com>
CppMicroServices/CppMicroServices,CppMicroServices/CppMicroServices,CppMicroServices/CppMicroServices,CppMicroServices/CppMicroServices,CppMicroServices/CppMicroServices,saschazelzer/CppMicroServices,saschazelzer/CppMicroServices