flutter Your app isn't using AndroidX

[!] Your app isn't using AndroidX.
    To avoid potential build failures, you can quickly migrate your app by following the steps on
    https://goo.gl/CP92wY.

解决这个警告的办法是在gradle.properties添加如下代码即可

android.enableJetifier=true
android.useAndroidX=true

原文：https://www.cnblogs.com/qqcc1388/p/12263094.html