title: Flutter requires SDK version
body: <p>I have this error:</p>
  <pre><code>Running &quot;flutter packages upgrade&quot; in bingo360...               
  The current Dart SDK version is 2.1.2-dev.0.0.flutter-0a7dcf17eb.
  Because bingo360 depends on flutter_launcher_icons &gt;=0.7.1 which requires SDK version &gt;=2.2.0 &lt;3.0.0, version solving failed.
  pub upgrade failed (1)
  </code></pre>
  <p>My pubspec.yaml is:</p>
  <pre><code>environment:
  sdk: &quot;&gt;=2.1.0 &lt;3.0.0&quot;
  
  dependencies:
    flutter:
      sdk: flutter
  
  cupertino_icons: ^0.1.2
  http: ^0.12.0+1
  flutter_launcher_icons: &quot;^0.7.2&quot;
  
  dev_dependencies:
    flutter_test:
    sdk: flutter
  </code></pre>
  <p>I try to change to <code>sdk: &quot;&gt;2.2.0 &lt;3.0.0&quot;</code> but not works.</p>
  <p>Any suggest?</p>