Correction for cluster example in my "Beginner's Guide OpenLayers 3" due to change in OpenLayers library itself

README.md

Due to request on Twitter https://twitter.com/Stephanux40/status/833289922777903104

There were two issues:

• change due to ol.source.GeoJSON removal in 3.5.0 https://github.com/openlayers/openlayers/releases/tag/v3.5.0 See section "New Vector API" for the exact documentation for upgrading.
• because the data from cluster.geojson is using projection 3857 instead of the default EPSG 4326, we needed to add in the new ol.format.GeoJSON the following:

  ..
  format: new ol.format.GeoJSON({
    defaultDataProjection: 'EPSG:3857'
  })
  ..

cluster.geojson

countries.geojson

index.html

samples.css