EPSG:4326 example broken

The [EPSG:4326 example](http://ol3js.org/en/master/examples/epsg-4326.html) is currently not working.  Requests for [tiles like this](http://vmap0.tiles.osgeo.org/wms/vmap0?SERVICE=WMS&VERSION=1.1.1&REQUEST=Ge%E2%80%A6=basic&WIDTH=256&HEIGHT=256&SRS=EPSG%3A4326&STYLES=&BBOX=-90%2C-90%2C0%2C0) result in:
```
loadSymbolSet(): Unable to access file. (/mapdata/vmap.sym)
```

Rather than fix this, it would be nice to show something prettier than vmap0.  @bartvde @ahocevar should we commit to this layer being available?
```js
  new ol.layer.Tile({
    source: new ol.source.TileWMS({
      url: 'http://demo.opengeo.org/geoserver/wms',
      params: {'LAYERS': 'ne:NE1_HR_LC_SR_W_DR'}
    })
  })
```