title: setMethodCallHandler never run on BeaconsPlugin for Flutter
body: <p>I want scan beacon devices, I'm using this plugin <a href="https://pub.dev/packages/beacons_plugin" rel="nofollow noreferrer">https://pub.dev/packages/beacons_plugin</a> . I wrote the code like plugin's example code but i only see 2 print in my console. I can't see 3. print and can't startMonitoring.</p>
  <pre><code>if (Platform.isAndroid) {
        //Prominent disclosure
        print('HELLO ANDROID');
        await BeaconsPlugin.setDisclosureDialogMessage(
                title: &quot;Title&quot;,
                message:
                    &quot;Message&quot;)
            .then((value) {
          print('HELLO ANDROID 2');
        });
        // await BeaconsPlugin.clearDisclosureDialogShowFlag(false);
        BeaconsPlugin.channel.setMethodCallHandler((call) async {
          print(&quot;Method: ${call.method}&quot;);
          if (call.method == 'scannerReady') {
            await BeaconsPlugin.startMonitoring();
          } else if (call.method == 'isPermissionDialogShown') {
            print(&quot;Prominent disclosure message is shown to the user!&quot;);
          }
        });
      } 
  </code></pre>