The vector-layer example does not work when hosted

See http://openlayers.github.com/ol3/master/examples/vector-layer.html

This is because it relies on test/spec/ol/parser/geojson/countries.json, which is not added to the gh-pages branch by the hostexamples build target.

We had the same problem for the wms capabillities example, which we fixed by copying the XML file (ogcsample.xml) into examples/data. We should do the same for countries.json.