code: function getDirContentMTime(dirPath, ignoredDirs, ignoredFiles){
      let mtime
      if(fs.existsSync(dirPath)){
          _ignoredDirs.push.apply(_ignoredDirs, ignoredDirs)
          _ignoredFiles.push.apply(_ignoredFiles, ignoredFiles)
          mtime = recursiveGetDirContentMTime(dirPath)
      }
      return mtime
  }
docs: get the last modification time of the directory including its files and subdirectories