geometry coordinates should be in EPSG:4326

[iosefa]

Problem
vuelayers will only play with EPSG:3857 or EPSG:4326 out of the box. The current is 2447.

Improvement
Transform the response to EPSG:4326.

Alternatives
We could also transform the response to EPSG:3857 and since this is often used for web maps. However, it is likely that transforming data to 4326 will be added to the django-rest-frameworkgis package: openwisp/django-rest-framework-gis#188 and so will eventually be usable out of the box. Thus if we make it 4326 we can then remove this fix once the package is updated.