title: Error adding Flutter web-view plugin in version 1.20.4
body: <p>I would like to use flutter-web plugin in my app. However, I am getting the following SDK error when I add it to my YAML file. I just upgraded to 1.20.4</p>
  <p>How do I fix this error?</p>
  <p>The current Flutter SDK version is 1.20.4.</p>
  <p>Because app depends on webview_flutter &gt;=1.0.0 which requires Flutter SDK version &gt;=1.22.0 &lt;2.0.0, version solving failed.
  pub get failed (1; Because app depends on webview_flutter &gt;=1.0.0 which requires Flutter SDK version &gt;=1.22.0 &lt;2.0.0, version solving failed.)</p>
  <p>Doctor summary (to see all details, run flutter doctor -v):
  [✓] Flutter (Channel stable, 1.20.4, on Mac OS X 10.15.6 19G2021, locale en-US)</p>
  <p>[✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
  [✓] Xcode - develop for iOS and macOS (Xcode 12.0)
  [✓] Android Studio (version 3.6)
  [✓] VS Code (version 1.49.2)
  [✓] Connected device (1 available)</p>
  <p>• No issues found!</p>
  <p>This is the info in my pubspec.yaml file</p>
  <p>environment:
  sdk: &quot;&gt;=2.2.2 &lt;3.0.0&quot;</p>