delete matplotlib.use("Agg")

[JingxianKe]

Agg只能生成图像文件，禁止弹出GUI交互图，不能满足部分人的需要。

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}