fix ?format=geojson for findBox()
fix ?format=geojson for findBox()

The previous implementation returned a point object within a FeatureCollection.
This is invalid GeoJSON, and updated turf.js does not allow this anymore.
Returning a FeatureCollection for a single point didn't make much sense anyway
sensebox/OpenSenseMap-API,mpfeil/OpenSenseMap-API,mpfeil/OpenSenseMap-API,sensebox/OpenSenseMap-API