Fix dependency conflict for issue

[NeolithEra]

#16

[NeolithEra]

@dylankilkenny Could you please help me review this issue?
Thank you very much!

BTW, dependency conflict problems are very common in practice in python ecosystem. I have encountered the issues several times. What's your oppinion on the challenges of detecting and repairing such issues? And how to avoid dependency conflict problems among python projects, especially from the ecosystem's perspective?

[joesixpack]

PR #14 and #15 fix it