code: function resolveOutputTarget(customPath, filename) {
      const realPath = path.resolve('.', customPath);
  
      const getPath = tryCatch(
          realPath => fs.lstatSync(realPath).isDirectory()
              ? path.join(realPath, filename)
              : realPath,
          identity);
  
      return getPath(realPath);
  }
docs: Taking account the -o parameter can be used to specify the output directory,
  let's deal with it
  
  @param {String} customPath
  @param {String} filename
  @return {String}