Using grpc via protobuf.cpp adds wrong grpc plugin path

Hello,

in the protobuf.cpp module the cpp.includePaths should be appended with the content of the grpcIncludePath variable if grpc will be used. But currently

    cpp.includePaths: {
        var result = [outputDir, includePath];
        if (useGrpc)
            result.push("grpcIncludePath");
        return result;
    }

it does not use the variable but appends the string "grpcIncludePath".