Fix so all GeooJSON returned is "valid" according to Koop

[jkerr5]

Koop complains about the service metadata because it is missing the type property:

WARNING: Source data for /marklogic/rest/services/<service name>/FeatureServer is invalid GeoJSON:
 	 1) "type" member required

The type property should be in the metadata and it can be just set to "".

[grtjn]

Is there a way to suppress this issue by making changes to descriptors? Not sure what is meant with setting 'type' to empty string...