flutter doctor踩坑 X Android license status unknown.

Windows 下配置flutter，运行 flutter doctor日志显示：

E:\AppData\FlutterSDK\flutter>flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[a??] Flutter (Channel stable, v1.12.13+hotfix.5, on Microsoft Windows [Version
   6.1.7601], locale zh-CN)
[!] Android toolchain - develop for Android devices (Android SDK version 29.0.2)

   X Android license status unknown.
     Try re-installing or updating your Android SDK Manager.
     See https://developer.android.com/studio/#downloads or visit
     https://flutter.dev/setup/#android-setup for detailed instructions.
[a??] Android Studio (version 3.5)
[!] IntelliJ IDEA Community Edition (version 2018.2)
   X Flutter plugin not installed; this adds Flutter specific functionality.
   X Dart plugin not installed; this adds Dart specific functionality.
[a??] Connected device (1 available)

! Doctor found issues in 2 categories.

X Android license status unknown.
网上一查，需要执行flutter doctor --android-licenses，顺利的话一路输入Y同意下去就OK
当然不顺利的话，会提示：

A newer version of the Android SDK is required. To update, run:
xxx(your 本地SDK路径)/sdk/tools/bin/sdkmanager --update

碰到这个问题，千万不要直接控制台输命令直接执行，时间很慢，并且还容易遇到Warning: An error occurred during installation: Failed to move away or delete existing target file: 这个报错.
这个时候，正确的姿势应该是打开安装AndroidSDK的目录找到SDKManager.exe去升级sdk tools 里的sdk tools, sdkplatform-Tools, sdk Build-Tools 这三个东西，
我升级的时候，SDKManager.exe打不开，只是闪了一下，最后是通过AndroidStudio的 setting==》Android SDK===》右边选择SDK Tools升级也可以。
升级完之后，继续执行上面的flutter doctor --android-licenses，一路Yes 下去就OK了。