OpenLayers unavaible in the deegree OGC API demo

[julianzz98]

Using the deegree OGC API demo under http://cite.deegree.org/deegree-ogcapi-1.3/datasets/strassenbaumkataster/collections/strassenbaumkataster/items, it seems that the feature preview map is unavailable.

The GET request URLs:

• https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io@master/en/v6.1.1/css/ol.css
• https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io@master/en/v6.1.1/build/ol.js
  both result in a HTTP status code 403.

This is most likely caused by the renaming of the master branch to main in the https://github.com/openlayers/openlayers.github.io repository.

The correct URLs should therefore be:

• https://github.com/openlayers/openlayers.github.io/blob/main/dist/en/v6.1.1/build/ol.js
• https://github.com/openlayers/openlayers.github.io/blob/main/dist/en/v6.1.1/css/ol.css

In this step, the version could potentially upgraded to https://github.com/openlayers/openlayers.github.io/tree/main/dist/en/v6.9.0

[tfr42]

relates to #53