Flutter_HTTP Host Availability

其实这个问题无关紧要，解不解决都行。
https://github.com/flutter/flutter/issues

[☠] HTTP Host Availability (the doctor check crashed)
    ✗ Due to an error, the doctor check did not complete. If the error message
      below is not helpful, please let us know about this issue at
      https://github.com/flutter/flutter/issues.
    ✗ HandshakeException: Connection terminated during handshake

[!] HTTP Host Availability
    ✗ HTTP host https://maven.google.com/ is not reachable. Reason: An error
      occurred while checking the HTTP host: Operation timed out
    ✗ HTTP host https://cloud.google.com/ is not reachable. Reason: An error
      occurred while checking the HTTP host: Operation timed out

解决步骤：

1、打开/path-to-flutter-sdk/packages/flutter_tools/lib/src/http_host_validator.dart文件，修改https://maven.google.com/为 google maven 的国内镜像，如https://maven.aliyun.com/repository/google/。
2、删除/path-to-flutter-sdk/bin/cache 文件夹
3、重新执行flutter doctor

其实这个问题无关紧要，解不解决都行。