尝试运行时，flutter build web当前不支持“构建网络”。我之前遇到过错误，Dart 2.5.0-dev.4.0.flutter-be66176534需要 2.5.0 或更高版本，现在已经解决了，但我无法构建我的项目。
flutter doctor -v
[?] Flutter (Channel stable, v1.9.1+hotfix.2, on Microsoft Windows [Version 10.0.18932.1000], locale en-GB)
• Flutter version 1.9.1+hotfix.2 at C:\src\flutter
• Framework revision 2d2a1ffec9 (8 days ago), 2019-09-06 18:39:49 -0700
• Engine revision b863200c37
• Dart version 2.5.0
[?] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
• Android SDK at C:\Users\germa\AppData\Local\Android\sdk
• Android NDK location not configured (optional; useful for native profiling support)
• Platform …