Update xfdown_api.py

Replace print() with _print()

Fix this issue
  File "/home/jiasui/repos/xfdown/xfdown_api.py", line 274, in getlist
    print (_('无离线任务!'))UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-4: ordinal not in range(128)
Merge pull request #16 from jsfaint/patch-1

Update xfdown_api.py