title: Exception running command on UI thread
body: <p>I add <a href="https://prime31.com/docs#androidPlayGameServices" rel="nofollow">Prime31</a> plugin for GooglePlayGameServices but it don't want to authenticate and send an error: "Exception running command on UI thread"</p>
  
  <pre><code>if( GUILayout.Button( "Authenticate" ) )
              {
                  PlayGameServices.authenticate();
              }
  
  public static void authenticate()
          {
              if( Application.platform != RuntimePlatform.Android )
                  return;
  
              _plugin.Call( "authenticate" );
          }
  </code></pre>
  
  <p>And I did all <a href="https://prime31.com/docs#androidPlayGameServices" rel="nofollow">this</a> tutorial steps.</p>