def fetch_file(file = Lock::FILE_NAME, ref = REF, new_line = NEW_LINE)
      super(file, ref, new_line)
    end
def fetch_file(file = Lock::FILE_NAME, ref = REF, new_line = NEW_LINE)
      super(file, ref, new_line)
    end
@param file [String] target file
 @param ref [String] git ref
 @param new_line [String] file's ending new line

 @return [String] target file contents