命令flutter packages get有效，但是flutter packages upgrade失败，
flutter packages upgrade
Running "flutter packages upgrade" in *****...
Git error. Command: git fetch
fatal: unable to look up github.com (port 9418)
关于我在设置中遇到的问题的任何想法吗？
flutter packages upgrade -v
[ +54 ms] executing: [****] git rev-parse --abbrev-ref --symbolic @{u}
[ +105 ms] Exit code 0 from: git rev-parse --abbrev-ref --symbolic @{u}
[ +3 ms] origin/beta
[ ] executing: [****] git rev-parse --abbrev-ref HEAD
[ +59 ms] Exit code 0 from: git rev-parse --abbrev-ref HEAD
[ ] beta
[ ] executing: [****] git ls-remote --get-url origin
[ +49 ms] Exit code 0 from: git ls-remote --get-url origin
[ ] https://github.com/flutter/flutter.git
[ ] executing: [****] git log -n 1 --pretty=format:%H
[ +87 ms] Exit code 0 from: git log -n 1 --pretty=format:%H
[ ] 5391447fae6209bb21a89e6a5a6583cac1af9b4b
[ ] executing: [****] git log -n 1 --pretty=format:%ar
[ +79 ms] Exit code 0 from: git log -n 1 --pretty=format:%ar
[ ] 6 days ago
[ +1 ms] executing: [***] git describe --match v*.*.* --first-parent --long --tags
[ +749 ms] Exit code 0 from: git describe --match v*.*.* --first-parent --long --tags
[ ] v1.0.0-0-g5391447fa
[ +290 ms] Running "flutter packages upgrade" in *****...
[ +18 ms] executing: [****] *****\flutter\bin\cache\dart-sdk\bin\pub.bat --verbosity=warning --verbose upgrade --no-precompile
[+3013 ms] Git error. Command: git fetch
[ +3 ms] fatal: unable to look up github.com (port 9418) (Programmet har ikke kalt WSAStartup, eller WSAStartup mislyktes. )