title: Flutter how show markers in the circle? flutter_map
body: <p>newbie in Flutter. How show markers in the circle in flutter_map. Which day already trying to solve this problem. I can't make the markers in the radius change, or just change color. That's what i have achieved:</p>
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>Position _currentPosition;
    static final List&lt;LatLng&gt; _points = [
      LatLng(55.749122, 37.659750),
      LatLng(55.770854, 37.626963),
      LatLng(55.776937, 37.637949),
      LatLng(55.739266, 37.637434),
    ];
  
    static const _markerSize = 40.0;
    List&lt;Marker&gt; _markers;
    List&lt;CircleMarker&gt; circle;
  
    @override
    void initState() {
      super.initState();
  
      _markers = _points
          .map(
            (LatLng point) =&gt; Marker(
          point: point,
          width: _markerSize,
          height: _markerSize,
          builder: (_) =&gt; Icon(Icons.location_on, size: _markerSize),
        ),
      ).toList();
  
      _getCurrentLocation();
    }
  
    _getCurrentLocation() {
      geolocator
          .getCurrentPosition(desiredAccuracy: LocationAccuracy.best)
          .then((Position position) {
        setState(() {
          _currentPosition = position;
        });
  
      }).catchError((e) {
        print(e);
      });
    }
  
    @override
    Widget build(BuildContext context) {
      return FlutterMap(
        options: new MapOptions(
            minZoom: 16.0,
            center:  new LatLng(_currentPosition.latitude,_currentPosition.longitude)),
        layers: [new TileLayerOptions(urlTemplate: 'https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png',
            subdomains: ['a','b','c']),
          new MarkerLayerOptions(
              markers: [
                new Marker(
                    width: 45.0,
                    height: 45.0,
                    point: new LatLng(_currentPosition.latitude,_currentPosition.longitude),
                    builder: (context)=&gt;new Container(
                      child: IconButton(icon: Icon(Icons.accessibility), onPressed: () {print('Marker tapped!');}),
                    ))]),
        MarkerLayerOptions(markers: _markers),
        CircleLayerOptions(circles: [ CircleMarker(
            point: LatLng(_currentPosition.latitude,_currentPosition.longitude),
            color: Colors.blue.withOpacity(0.7),
            borderStrokeWidth: 2,
            useRadiusInMeter: true,
            radius: 2000 // 2000 meters | 2 km
        )]),
      ],
      );
    }</code></pre>
  </div>
  </div>
  </p>
  <p><a href="https://i.stack.imgur.com/7n6JD.jpg" rel="nofollow noreferrer">my result - (this is image)</a></p>
  <p>How to change the markers in the blue circle. For example change the marker icon?</p>