title: I cannot run my flutter app. It says Flutter requires Android SDK 28, and I have sdk 28
body: <p>when I run flutter doctor, it shows me the following errors:</p>
  
  <pre><code>Running flutter doctor...
  Doctor summary (to see all details, run flutter doctor -v):
  [?] Flutter (Channel stable, v1.2.1, on Microsoft Windows [Version 10.0.17134.112], locale en-US)
  [!] Android toolchain - develop for Android devices (Android SDK version 27.0.3)
      X Flutter requires Android SDK 28 and the Android BuildTools 28.0.3
        To update using sdkmanager, run:
          D:/Tools/sdk\tools\bin\sdkmanager "platforms;android-28" "build-tools;28.0.3"
        or visit https://flutter.io/setup/#android-setup for detailed instructions.
      X Android license status unknown.
  [?] Android Studio (version 3.3)
  [!] IntelliJ IDEA Ultimate Edition (version 2017.1)
      X Flutter plugin not installed; this adds Flutter specific functionality.
      X Dart plugin not installed; this adds Dart specific functionality.
  [?] VS Code (version 1.26.1)
  [?] Connected device (1 available)
  </code></pre>