title: flutter doctor --android-licenses does not work
body: <p>when I run <code>flutter doctor</code> I noticed license status is unknown.</p>
  
  <pre><code>[√] Flutter (Channel stable, v1.0.0, on Microsoft Windows [Version 10.0.17763.253], locale en-US)
  [!] Android toolchain - develop for Android devices (Android SDK 28.0.3)
      X Android license status unknown.
  [√] Android Studio (version 3.3)
  [√] IntelliJ IDEA Ultimate Edition (version 2018.3)
  [!] VS Code (version 1.30.2)
  [!] Connected device
      ! No devices available
  
  ! Doctor found issues in 3 categories.
  </code></pre>
  
  <p>I found that in order to resolve the license I need to run this command <code>flutter doctor --android-licenses</code>. when I run that I get the following error: </p>
  
  <pre><code>The system cannot find the path specified.
  The system cannot find the path specified.
  The system cannot find the path specified.
  A newer version of the Android SDK is required. To update, run:
  C:\Users\myusername\AppData\Local\Android\sdk\tools\bin\sdkmanager --update
  </code></pre>
  
  <p>So I then tried running <code>C:\Users\myusername\AppData\Local\Android\sdk\tools\bin\sdkmanager --update</code> I received the below error:</p>
  
  <pre><code>'E\AppData\Local\Android\Sdk\tools\bin\' is not recognized as an internal or external command,
  operable program or batch file.
  Error: Could not find or load main class com.android.sdklib.tool.sdkmanager.SdkManagerCli
  </code></pre>
  
  <p>I looked everywhere online and could not find any answer. I am new to flutter and do not know how to resolve this problem. Any help would be great thanks!</p>