Attribution not according to OSM policy

[stkdiretto]

See openstreetmap/openstreetmap-website#838 – the attribution label merely states “Tiles courtesy of Andy Allan”, which leads to embedded maps showing only this information, omitting the required “© OpenStreetMap contributors”.

This is a problem, since it makes users inadvertently infringe on OSM copyright when using the standard OSM embed code, which in turn relies on this script.