Update ConcurrencyTest.cpp (#374)
Update ConcurrencyTest.cpp (#374)

Fixes #370
CppMicroServices/CppMicroServices,CppMicroServices/CppMicroServices,CppMicroServices/CppMicroServices,CppMicroServices/CppMicroServices,saschazelzer/CppMicroServices,saschazelzer/CppMicroServices,CppMicroServices/CppMicroServices