Center Map on Layer Change in Leaflet

## index.html
<!DOCTYPE html>
<meta charset="utf-8">
<html>
<head>
  <link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-0.6.4/leaflet.css" />
  <!--[if lte IE 8]>
      <link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-0.6.4/leaflet.ie.css" />
  <![endif]-->
  <script src="http://cdn.leafletjs.com/leaflet-0.6.4/leaflet.js"></script>

  <style type="text/css">
  #map {
    height: 500px;
  }
  </style>
</head>
<body>

<h1></h1>
<div id="map"></div>
<script type="text/javascript">

  var circle = L.circle([51.508, -0.11], 500, {
      color: 'red',
      fillColor: '#f03',
      fillOpacity: 0.5
  });

  var polygon = L.polygon([
      [51.509, -0.08],
      [51.503, -0.06],
      [51.51, -0.047]
  ]);

  var map = L.map('map', {
    center: [51.505, -0.09],
    zoom: 13
  });

  var overlayMaps = {
    "Circle": circle,
    "Polygon": polygon
  };

  L.tileLayer('http://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {
    attribution: '&copy; <a href="http://openstreetmap.org">OpenStreetMap</a> contributors, <a href="http://creativecommons.org/licenses/by-sa/2.0/">CC-BY-SA</a>'
  }).addTo(map);

  L.control.layers(overlayMaps, null, {
    collapsed: false
  }).addTo(map);

  // recenter map on base layer change:
  map.on('baselayerchange', function(e) {
    console.log(e);
    map.fitBounds(e.layer);
  });

</script>

</body>
</html>