Collect coverage with gcc6
Collect coverage with gcc6

The output generated by GCC 8 and 9 is confusing the coveralls script
when C++ templates are involved and it generates bogus reports (shows
lines without code as being executed multiple times, or red - without
coverage):

https://coveralls.io/builds/26775071/source?filename=src/client.cc#L494

https://travis-ci.org/vasild/cpp-ipfs-http-client/builds/607739355#L1524

        -:  476:template <class PropertyType>
       22:  477:void Client::GetProperty(const Json& input, const std::string& property_name,
        -:  478:                         size_t line_number, PropertyType* property_value) {
       22:  479:  if (input.find(property_name) == input.end()) {
        -:  480:    throw std::runtime_error(
        -:  481:        std::string("Unexpected reply: valid JSON, but without the \"") +
        -:  482:        property_name + "\" property on line " + std::to_string(line_number) +
       1*:  483:        ":\n" + input.dump());
        -:  484:  }
        -:  485:
       21:  486:  *property_value = input[property_name];
       21:  487:}
------------------
_ZN4ipfs6Client11GetPropertyINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEEEvRKN8nlohmann10basic_jsonISt3mapSt6vectorS7_blmdSaNS8_14adl_serializerEEERKS7_mPT_:
       17:  477:void Client::GetProperty(const Json& input, const std::string& property_name,
        -:  478:                         size_t line_number, PropertyType* property_value) {
       17:  479:  if (input.find(property_name) == input.end()) {
        -:  480:    throw std::runtime_error(
        -:  481:        std::string("Unexpected reply: valid JSON, but without the \"") +
        -:  482:        property_name + "\" property on line " + std::to_string(line_number) +
    #####:  483:        ":\n" + input.dump());
        -:  484:  }
        -:  485:
       17:  486:  *property_value = input[property_name];
       17:  487:}
------------------
_ZN4ipfs6Client11GetPropertyIN8nlohmann10basic_jsonISt3mapSt6vectorNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEblmdSaNS2_14adl_serializerEEEEEvRKSD_RKSB_mPT_:
        5:  477:void Client::GetProperty(const Json& input, const std::string& property_name,
        -:  478:                         size_t line_number, PropertyType* property_value) {
        5:  479:  if (input.find(property_name) == input.end()) {
        -:  480:    throw std::runtime_error(
        -:  481:        std::string("Unexpected reply: valid JSON, but without the \"") +
        -:  482:        property_name + "\" property on line " + std::to_string(line_number) +
        1:  483:        ":\n" + input.dump());
        -:  484:  }
        -:  485:
        4:  486:  *property_value = input[property_name];
        4:  487:}

vasild/cpp-ipfs-api,vasild/cpp-ipfs-api