siyuhong

fix the log file path error when using system environment variables in log.conf

2

system : ubuntu20 compiler : x86_64-linux-gnu g++ compiler version : 9.4.0 build error : undefined reference to 'Log4Qt::AppenderAttachable::~AppenderAttachable()'

` Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly or one of its dependencies. File name: 'System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' at SerialPCAP.AssemblyExtensions.Description () [0x00005] in :0 at SerialPCAP.MainClass.ShowHelp (Mono.Options.OptionSet...